gh-98401: Invalid escape sequences emits SyntaxWarning (#99011)

gh-98401: Invalid escape sequences emits SyntaxWarning (#99011)

A backslash-character pair that is not a valid escape sequence now
generates a SyntaxWarning, instead of DeprecationWarning.  For
example, re.compile("\d+\.\d+") now emits a SyntaxWarning ("\d" is an
invalid escape sequence), use raw strings for regular expression:
re.compile(r"\d+\.\d+"). In a future Python version, SyntaxError will
eventually be raised, instead of SyntaxWarning.

Octal escapes with value larger than 0o377 (ex: "\477"), deprecated
in Python 3.11, now produce a SyntaxWarning, instead of
DeprecationWarning. In a future Python version they will be
eventually a SyntaxError.

codecs.escape_decode() and codecs.unicode_escape_decode() are left
unchanged: they still emit DeprecationWarning.

* The parser only emits SyntaxWarning for Python 3.12 (feature
  version), and still emits DeprecationWarning on older Python
  versions.
* Fix SyntaxWarning by using raw strings in Tools/c-analyzer/ and
  wasm_build.py.