The time profiler in `Expr::isIntegerConstantExpr` used to
call `Loc->printToString`, it was inconsistent with other time
profiles in the file and caused segfaults if `Loc` was `nullptr`.
Fixes https://github.com/llvm/llvm-project/issues/58551
Reviewed By: dyung, jloser
Differential Revision: https://reviews.llvm.org/D136549
Add time profiler for various constexpr evaluation events
so that slow event could be visible on the visualized flame chart.
Reviewed By: aaron.ballman
Differential Revision: https://reviews.llvm.org/D136022