[backport] SI-7470 implements fundep materialization

Backports 21a8c6c from the 2.11.x branch under -Xfundep-materialization
as per Miles Sabin's request. Thanks Miles!
pull request feedback
SI-8803 generate super accessor for super[A], if A is outer superclass

    class C extends A with T {
      class I {
        C.super[T]
        C.super[A]
      }
    }

A super call in a nested class of the form super[T] where T is a
parent trait of the outer class doesn't need an accessor: mixin can
directly re-route the call to the correct implementation class - it's
statically known to be T$class.

However, if a nested class accesses super[A] and A is the superclass
of the outer class (not a trait), then we need a super accessor in the
outer class.

We need to add the mixin name to the super accessor name, otherwise
it clashes with non-qualified super accessors.
SI-8474  Inconsistent behavior of patch method

Changed Iterator to be consistent with other collections.

Also fixed SeqViewLike to validate/constrain inputs.

No specific tests; quasi-comprehensive collection tests will cover this later.
SI-5254 running an empty scala script should succeed

The script runner made the assumption that "compilation succeeded"
implies "there is a Main class to run", but this can be wrong if the
script is empty (or only contains imports/comments).

The ScriptRunner now uses the ClassPath utility to check if there really
is a main class. If not, it doesn't try to run it and returns
peacefully. This also makes `scala -e ''` succeed.
Fix assertThrows, and the behaviors that it shadowed

The test in StdNamesTest was introduced in cff8b569, where newTermName
would throw on a negative length. In b090f97 this was changed to fix
the negative length, but the test was not adapted (as it didn't fail).
-Ystatistics accepts a list of phases, cleanups in MultiChoiceSetting

MultiChoiceSetting and Xlint with its deprecated aliases is now a bit
simpler, but there's still room for improvement, as noted in comments.
Add flag to disable withFilter pattern desugaring

This adds a flag called `-Zirrefutable-generator-patterns` which changes
desugaring of code like the following:

    for {
      (a, b) <- List(1 -> 'a', 2 -> 'b')
      (c, d) <- List(3 -> 'c', 4 -> 'd')
    } yield (a + c, b + d)

Which previously would turn into something like:

    List(1 -> 'a', 2 -> 'b').withFilter {
      case (a, b) => true
      case _ => false
    }.flatMap {
      case (a, b) =>
        List(3 -> 'c', 4 -> 'd').withFilter {
          case (c, d) => true
          case _ => false
        }.map {
          case (c, d) =>
            (a + c, b + d)
        }
    }

With this new flag, it only becomes:

    List(1 -> 'a', 2 -> 'b').flatMap {
      case (a, b) =>
        List(3 -> 'c', 4 -> 'd').map {
          case (c, d) =>
            (a + c, b + d)
        }
    }

Which creates a few benefits:

1. We don't have to do a useless call to withFilter
2. We can use patterns on things without withFilter
3. Things don't silently disappear when patterns are wrong
Warn on non-exhaustive for-comprehension patterns

We assume patterns are exhaustive when desugaring with
`-Zirrefutable-generator-patterns` but we should still emit a warning if
we think they might not be.
Add a test for -Zirrefutable-generator-patterns
List Typelevel options when -Z flag is given
Merge pull request #3935 from lrytz/t8803

SI-8803 generate super accessor for super[A], if A is outer superclass
SI-8806 Add lower bound check to Any lint

We already exclude the lint check for infer-any if
Any is somewhere explicit.

This commit adds lower bounds of type params to
the somewheres.

Motivated by:

```
scala> f"${42}"
<console>:8: warning: a type was inferred to be `Any`; this may indicate a programming error.
              f"${42}"
                  ^
res0: String = 42
```
Use Enumeration for MultiChoiceSetting

This is pretty easy, since a ValueSet is a BitSet.

When the setting is updated, recompute the current
set of values, which is cheap and succinct.

Checking a flag is also easy and fast.

Choices in MultiChoiceSettings may enable other choices.
Fix broken URL for MathJAX Javascript dependency.

Loaded using an DNS alias for the CDN, as per the
[instructions](http://docs.mathjax.org/en/latest/configuration.html)

I also switched from `latest` to `2.3-latest`, so that we don't
automatically perform major upgrades.
Address PR feedback, fix MultiChoiceSetting.contains
Make MultiChoiceSetting.compute easier to understand
Merge pull request #3939 from lrytz/ystats

-Ystatistics accepts a list of phases for which to print stats
Merge pull request #3801 from Ichoran/issue/8474

SI-8474  Inconsistent behavior of patch method
Merge pull request #3946 from gourlaysama/wip/t5254

SI-5254 running an empty scala script should succeed