Changes:
- Fix read_value_type description.
- Make sure read_value_type always emits an error for an invalid type.
  Remove checks for errors at call sites.
- (Drive-by) Fix validation flags in DecodeLocals.

Change-Id: I82bd8a61f0e26f39506fc6e4ab4be331dfe24ad7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2526390
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71233}