Generated-file exclusion by filename pattern

Intent

Machine-generated sources - Qt moc output, protobuf stubs, and the output of other code generators - often should not appear in the compilation database, so that linters and editors act only on hand-written code. A user can list filename patterns that exclude (or re-include) matching source files. This is off by default: with no such configuration the output is unchanged.

Acceptance criteria

• A configuration option lists filename patterns, each with an include or exclude action. An entry whose source file matches an exclude pattern is omitted from the database.
• A pattern without a path separator matches the source file's basename; a pattern containing a separator matches the full source path as it appears in the entry.
• Rules are evaluated in order and the last matching rule wins, the same precedence the directory rules use (see output-source-directory-filter). A file matched by no pattern rule is included.
• File-pattern rules and directory rules compose: an entry is emitted only when both the directory rules and the file-pattern rules accept it.
• An invalid pattern is rejected during configuration validation with an error that identifies the offending rule.
• With no file-pattern rules configured, every entry the directory rules accept is emitted; behaviour is unchanged.

Testing

• Given events compiling main.cpp and moc_window.cpp, and a configuration excluding the basename pattern for moc_*.cpp, when bear runs, then the database contains main.cpp only.
• Given the same events and no file-pattern configuration, when bear runs, then the database contains both files.
• Given events compiling src/main.cpp and generated/main.cpp, and a configuration excluding the pattern generated/*.cpp, when bear runs, then the database contains src/main.cpp and omits generated/main.cpp: the pattern contains a path separator, so it is matched against the full source path rather than the basename.
• Given events compiling main.cpp and util.cpp, and a configuration with an exclude rule for *.cpp followed by an include rule for main.cpp, when bear runs, then the database contains main.cpp only: the later include rule re-includes it (last matching rule wins), while util.cpp stays excluded.
• Given events compiling src/main.cpp and src/moc_window.cpp, a directory rule including src, and a file-pattern rule excluding moc_*.cpp, when bear runs, then the database contains src/main.cpp and omits src/moc_window.cpp: an entry is emitted only when both the directory rules and the file-pattern rules accept it.
• Given a configuration containing a malformed pattern, when the configuration is validated, then validation fails with an error identifying the rule.

Rationale

• Generated-file filtering uses user-supplied globs