[Support] Apply `constexpr` to `getTypeName` (#127893)

This is a followup to 003a721c1c9e3a99d6d0c1a6755443b260235537, which we
noticed increased binary size a small but noticable amount. The increase
seems to be due to code size from each `llvm::getTypeName<T>` wrapper,
which adds up if there are a lot of types.

The original motivation was to improve runtime and avoid `getTypeName`
being recomputed each time. The implementation is simple enough that we
can make it fully constexpr, which addresses the size increase, but also
further improves runtime: we directly reference the data instead of
jumping through a guard variable to see if we've computed it already.

0 files changed, 0 insertions, 0 deletions