constexpr-ify some tests

using variants of
  git grep "^const char k" | grep test.cc | awk -F ':' '{print $1}' | sort | uniq | xargs sed -i 's/^const char /constexpr char /g'
and then repeating the same with each of
  uint8_t, uint32_t, uint16_t, size_t, int8_t, int16_t, int32_t, int64_t, double, uint64_t, unsigned int, float

Bug: webrtc:429563452
Change-Id: I55e6876fceeaa467eeaa7f877b6067b6299991dc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/404261
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#45497}