harden test case to avoid parsing failure when name is keyword
refactor out common logic between various statSeq-s in parser

Partial functions are left outside of the call to statSeq to allow
re-use and overriding capabilities for quasiquotes.
refactor out range position utility constructors

This will help to re-use same logic for creating range positions even
if atPos isn't used to assign position to the tree.
SI-6841 SI-6657 add support for packages into quasiquotes and toolbox

In order to implement this a new parser entry point
`parseStatsOrPackages` that augments current parseStats with ability
to parse "package name { ... }" syntax.
minor changes due to typos
use regular macro expansion logic for unapply quasiquotes

Previously due to limited support for expansion in apply position
quasiquotes had to use a compiler hook for deconstruction.

Now it's possible to eliminate that special treatment and use
regular macro expansion logic instead.
improved handling of fresh names in quasiquotes

Parser tends to often generate random names for intermediate
synthetic trees like LabelDefs in while loops. Previously such
names were reified as is and it caused name clash problems.

Now quasiquotes reify such names into calls to fresh name generator
thus ensuring that within the same compilation unit such problems
won't occur.

In pattern matching role such names are instead replaced by free
variables with consistency checks if the same name occurs multiple
times in the tree.
make q"f(..$xs)" deconstruction symmetrical to q"f[..$xs]"

Now both return empty list for $xs when tree doesn't have
any applications/type applications.
better name for isCaseDefStart

As it was pointed out by @paulp current isCaseDefStart method's name
doesn't really correspond to one of it's primary usages: checking if
the block within case has reached it's end.
fix minor regression in quasiquote reification

noSelfType should always be reified as noSelfType. After the the
introduction of SyntacticValDef this ceased to be true.
rename selfdef into selfType

For sake of consistency with noSelfType.