Function inline

This transformer will simplify the AST by doing trivial inlining operations.

It will:

1. Inline single-alternative alternations in concatenation (e.g. a(?:b)c => abc).
2. Inline single-alternation concatenations (e.g. (?:(?:a|b)|c) => (?:a|b|c)).
3. Inline constant-one quantifiers (e.g. ab{1}c => abc).
4. Remove constant-zero quantifiers (e.g. ab{0}c => ac).
5. Inline trivially nested assertions (e.g. (?!(?<!a)) => (?<=a)).
6. Inline nested assertions at the end of the expression tree (e.g. (?!a(?=b)) => (?!ab)).

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This transformer should be used in combination with removeDeadBranches to handle trivial simplifications.