Backport #22611
The code for checking if a commit has caused a change in a PR is
extremely inefficient and affects the head repository instead of using a
temporary repository.
This PR therefore makes several significant improvements:
* A temporary repo like that used in merging.
* The diff code is then significant improved to use a three-way diff
instead of comparing diffs (possibly binary) line-by-line - in memory...
Ref #22578
Signed-off-by: Andrew Thornton <art27@cantab.net>
The main purpose is to refactor the legacy `unknwon/com` package.
1. Remove most imports of `unknwon/com`, only `util/legacy.go` imports the legacy `unknwon/com`
2. Use golangci's depguard to process denied packages
3. Fix some incorrect values in golangci.yml, eg, the version should be quoted string `"1.18"`
4. Use correctly escaped content for `go-import` and `go-source` meta tags
5. Refactor `com.Expand` to our stable (and the same fast) `vars.Expand`, our `vars.Expand` can still return partially rendered content even if the template is not good (eg: key mistach).
zeripath