Add support for pipe placeholder `_` introduced in R language 4.2
Add support for pipe placeholder `_` introduced in R language 4.2:
- [x] Add support to R lexer
- [x] Add support to R parser
- [x] Add support to arg matching algorithm
- [x] Take it into account in SourceAnalyzer
- [x] Add error detection and reporting
- [x] Add support to syntax highlighting
- [x] Add support to expr index computation
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