[analyzer] Re-enable C++17-specific RVO construction contexts.

[analyzer] Re-enable C++17-specific RVO construction contexts.

Not contexts themselves, but rather support for them in the analyzer.

Such construction contexts appear when C++17 mandatory copy elision occurs
while returning an object from a function, and presence of a destructor causes
a CXXBindTemporaryExpr to appear in the AST.

Additionally, such construction contexts may be chained, because a return-value
construction context doesn't really explain where the object is being returned
into, but only points to the parent stack frame, where the object may be
consumed by literally anything including another return statement. This
behavior is now modeled correctly by the analyzer as long as the object is not
returned beyond the boundaries of the analysis.

Differential Revision: https://reviews.llvm.org/D47405

llvm-svn: 334684