Add compile-time validation of regular expressions.

[rsmmr]

So far we would catch pattern errors only at runtime. Now we report
the following at compile time if it can be statically determined:

• Patterns that don't compile (e.g., due to syntax errors)
• Use of $N referring to a capture group that exceeds the number a pattern defines.
• Use of `$Nq with a regular expression specifying multiple patterns
  for parallel matching (in which case group numbers are ill-defined).
• Use of $N with a &nosub field.

Closes #2131.

• Add a couple of static analysis methods to regular expression patterns.
• Add compile-time validation of regular expressions.

[codspeed-hq]

Merging this PR will not alter performance

✅ 28 untouched benchmarks

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_{Comparing topic/robin/gh-2131-capture-check (c6917d9) with main (1c5b216)}