The previous implementation of `WithParser` used regex, which struggles
with parsing nested structures correctly. This commit improves
`WithParser` to track and parse all nested `with` expressions.
Other improvements:
- Throw meaningful errors when syntax is wrong. Replacing the prior
behavior of silently ignoring such issues.
- Remove `I` prefix from related interfaces to align with newer code
conventions.
- Add more unit tests for `with` expression.
- Improve documentation for templating.
- `ExpressionRegexBuilder`:
- Use words `capture` and `match` correctly.
- Fix minor issues revealed by new and improved tests:
- Change regex for matching anything except surrounding
whitespaces. The new regex ensures that it works even without
having any preceeding text.
- Change regex for capturing pipelines. The old regex was only
matching (non-greedy) first character of the pipeline in tests,
new regex matches the full pipeline.
- `ExpressionRegexBuilder.spec.ts`:
- Ensure consistent way to define `describe` and `it` blocks.
- Replace `expectRegex` tests, regex expectations test internal
behavior of the class, not the external.
- Simplified tests by eliminating the need for UUID suffixes/prefixes.
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