[clang-format] Support of TableGen statements in unwrapped line parser (#78846)

Make TableGen's statements to be parsed considering their structure.
- Avoid to parse label
- Avoid class from being parsed as c++'s class
- Support if statement of the form `if <cond> then { ... }` 
- Support defset statement of the form `defset <type> <name> {}`

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Co-authored-by: Björn Schäpers <github@hazardy.de>