Fix SI-7130: Memory leaked caused by Statistics

As described in the ticket, we were leaking memory by holding reference
to Global through by-name argument that was captured by an instance of
a class stored in global HashMap `qs`.

The fix is simple: do not register quantities in HashMap unless statistics
is enabled. This way, if Statistics is disabled we do not store any
references.

We still leak memory in case of statistics being enabled.
make Future scaladoc examples up-to-date and compilable
SI-5744 evidence params are now SYNTHETIC

The macro def <-> macro impl correspondence check compares names of the
corresponding parameters in def and impl and reports an error if they
don't match. This was originally designed to avoid confusion w.r.t named
arguments (which ended up being never implemented as described in SI-5920).

Sometimes parameter names are generated by the compiler, which puts the
user in a tough position. Luckily, there's an escape hatch built it, which
omits the name correspondence check if one of the parameters is SYNTHETIC.
Everything went well until we realized that evidences generated by
context bounds aren't SYNTHETIC, which led to the bug at hand.

Marking auto-generated evidence parameters SYNTHETIC was only the first
step, as the correspondence checker uses parameter symbols, not parameter
trees. Why's that a problem? Because SYNTHETIC doesn't get propagated from def
trees to their underlying symbols (see ValueParameterFlags).

Unfortunately one cannot just change ValueParameterFlags, because that
would break printouts generated in TypeDiagnostics, which is designed to not
print synthetic symbols. Thus we modify methodTypeErrorString in
TypeDiagnostics to always print synthetic symbols.

Therefore now we propagate all paramSym.flags when doing correspondent sweeps
to keep them in sync between def trees and their underlying symbols. This
fixes the problem.
Merge pull request #2132 from u-abramchuk/SI5744

SI-5744 evidence params are now SYNTHETIC
Removing disabled, unneeded futures tests
unit test ide-t1000567 exercises SI-5063, aka #1000567.
Merge pull request #2131 from jozic/scaladoc-cleanup

make Future scaladoc examples up-to-date and compilable
Merge pull request #2135 from heathermiller/futures-cleanups

Removing disabled, unneeded futures tests
Merge pull request #2137 from huitseeker/issue/value-protected-in-inherited-1000567

SI-5013 / #1000567 : added presentation test for fixed bug
Merge pull request #2130 from vigdorchik/relax_doc

SI-7134: don't require doc.Settings in base api of scaladoc.
Merge pull request #2136 from vigdorchik/scanners

SI-7143 Fix scanner docComment production.
Merge pull request #2129 from gkossakowski/issues/SI-7130-Statistics

Fix SI-7130: Memory leaked caused by Statistics
Generalize the API to get docComments: allow to force docTrees
for entire hierarchy.