PR18217: Rewrite JumpDiagnostics' handling of temporaries, to correctly handle
declarations that might lifetime-extend multiple temporaries. In passing, fix a
crasher (PR18217) if an initializer was dependent and exactly the wrong shape,
and remove a bogus function (Expr::findMaterializedTemporary) now its last use
is gone.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@197103 91177308-0d34-0410-b5e6-96231b3b80d8