SI-8229 Source compatible name for implicit any2stringadd

To support the established pattern for disabling it for
an compilation unit.

Update scaladoc's knowledge of our "typeclasses".

Leave a `private[scala]` version of `StringAdd` (public in bytecode)
to ensure binary compatibility with 2.11.0-M8 for partest.
SI-7788 Avoid accidental shadowing of Predef.conforms

Rename `conforms` to `$conforms` and put in a minimal backstop: pos/t7788.scala

TODO: predicate the backwards compatibility shim for `Predef_conforms`
on `-Xsource:2.10`
SI-4577 singleton type pattern test should use `eq`, not `==`

I find it hard to imagine anyone is relying on `case x: foo.type =>`
erroneously being compiled to `foo == x` instead of the spec'ed `foo eq x`,
so let's finally fix this.
SI-8224 Fix regression in f-bound aware LUBs

Disable the heuristic approach to recursive bounds unless
the compiler is running under `-Xstrict-inference`.
[the above was not authored by the original author]

In db46c71e88, steps were taken to avoid blowing up in the
pathological LUB calculation needed for:

    def trav = List(List(), Stream())

This skipped a level in the base class sequence when f-bounds
were detected at the current level.

In that example, when `lublist` was about to:

    mergePrefixAndArgs(
      typeOf[LinearSeqOptimized[A, List[A]]],
      typeOf[LinearSeqOptimized[A, Stream[A]]],
    )

If it proceeded (as in 2.10.3), the LUB is invalid:

    error: type arguments [B[_ >: D with C <: B[_ >: D with C <: A]],s.c.immutable.LinearSeq[B[_ >: D with C <: A]] with s.c.AbstractSeq[B[_ >: D with C <: A]] with s.c.LinearSeqOptimized[B[_ >: D with C <: A],s.c.immutable.LinearSeq[A] with s.c.AbstractSeq[A] with s.c.LinearSeqOptimized[A,Immutable with Equals with java.io.Serializable] with java.io.Serializable] with java.io.Serializable] do not conform to trait LinearSeqOptimized's type parameter bounds [+A,+Repr <: s.c.LinearSeqOptimized[A,Repr]]

To avoid this, the added code would skip to the first non-F-bounded
base type of the same arity of each element in the list. This would
get to:

    LinearSeqLike[D, Stream[D]]
    LinearSeqLike[C, List[C]]

which are lubbable without violating the type constraints.

I don't think this was the right remedy. For starters, as seen in
this bug report, SI-8224, if the list of types are identical we
have let a perfectly good lub slip through our fingers, and end up
calculating too general a type.

More generally, if the type arguments in f-bounded positions coincide,
we don't risk calculating a ill-bounded LUB.

Furthermore, the code was widening each of the types separately;
this isn't something we want to do within `if (isUniformFrontier)`.
AFAICT this was just wasteful and as all `ts0` start with the same
type symbol, so `typeConstructorList` should be uniform.

This commit restricts this base-class skipping to situations where
the argument inferred for an type argument that is used as an f-bound
is not:

    a) an existential (as created by `mergePrefixAndArgs` in invariant
      positions.), or
    b) equivalent to one of the corresponding input type arguments
       (this is the case that fixes the regression in pos/8224.scala)
SI-8306: handle SWITCH nodes with just default case

Handle properly SWITCH nodes that contain just a default case in optimizer
(ConstantOptimization). SWITCH with just default case is expressed as a
node with empty tags and exactly one label. We can handle such nodes
easily by introducing a shortcut in logic that computes reachableLabels.

Add a test case which triggers patmat to generate SWITCH node with just
a default case.

Fixes SI-8306.
Attributed val/var processing for syntactics (SI-8180)
TypedTreesPrinter added
changes based on pull request comments:
print root packages flag; tests for syntactics; SyntacticEmptyTypeTree added to Printers
printers flag processing improvements: printRootPkg flag fixed, comments to flags metadata printing added
lazy vals printing fixed for typechecked trees
CodePrinter: TypedTreePrinter merged with ParsedTreePrinter
move methods for typechecked trees processing to TreeInfo
printOwners support added to Printers; whitespaces removed
block processing fixed for syntactics in typechecked trees
block wrapping for trees modified
fixes for wrappingIntoTerm
PrintersTest commented
Merge pull request #3560 from gkossakowski/issue/SI-8306

SI-8306: handle SWITCH nodes with just default case
SI-8197 Overload resolution should not consider default arguments

The spec says

> Let B be the set of alternatives in A that are applicable (§6.6)
> [...] It is an error if none of the members in B is applicable. If
> there is one single applicable alternative, that alternative is
> chosen. Otherwise, let C be the set of applicable alternatives which
> don’t employ any default argument in the application to e1, ..., em.
> It is again an error if C is empty. Otherwise, one chooses the most
> specific alternative among the alternatives in C [...].

There are many ways to interpret this, but none of them involves
excluding default getters, which is what the old code was doing.
We now exclude all alternatives that define any default arguments.

NOTE: according to SI-4728, this should fail to compile with an
ambiguity error. The compiler has been accepting this program
for all of 2.10.x, as far as I can tell, so let's not change that
for 2.11.0-RC1...
SI-6675 deprecation warning for auto-tupling in patterns

NOTE: when the deprecation warning becomes an error,
SI-6111 must become a `won't fix`
Fix quasiquote terminology to be consistent with Scheme

1. Rename cardinality into rank. Shorter word, easier to
   understand, more appropriate in our context.

2. Previously we called any dollar substitution splicing
   but this is not consistent with Scheme where splicing
   is substitution with non-zero rank.

   So now $foo is unquoting and ..$foo and ...$foo is
   unquote splicing or just splicing. Correspondingly
   splicee becomes unquotee.

3. Rename si7980 test into t7980
Tweak signature for quasiquote's apply

Even though quasiquotes are whitebox macros their
return values are in fact always trees. This might
help IDEs with macro expansions turned off.