[wasm][refactor] Tidy up errors in decoding

Changes:
- Add two additional PopTypeError overloads which take a C++/C-style
  string as argument over a ValueType.
- Change type errors in decoding to use PopTypeError. This improves
  consistency of error formatting as well as code readability.
- Improve some immediate argument errors.
- Adapt decoding unit tests.

Change-Id: Ifd54712965049a80692dbc3fde1ef489596e8662
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2614059
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71998}