Summary:
Remove ql_processor.h from headers that can do with just a forward declaration. This saves about 262 CPU seconds (26.2s on my M1 mac with 10 cores) of compile time according to ClangBuildAnalyzer.
Jira: DB-15930

Test Plan:
Ran `build daemons --no-ccache --clean` and ran ClangBuildAnalyzer to get the time output:
```
ClangBuildAnalyzer --all build/latest capture.out
ClangBuildAnalyzer --analyze capture.out > results.out
```

See the results before: {F343310}
Vs after (this header is no longer in the top 5 most expensive headers): {F343311}

Reviewers: ybase, hsunder

Reviewed By: hsunder

Subscribers: yql, hsunder

Differential Revision: https://phorge.dev.yugabyte.com/D42789