Enable more revive linter rules (#30608)

Noteable additions:

- `redefines-builtin-id` forbid variable names that shadow go builtins
- `empty-lines` remove unnecessary empty lines that `gofumpt` does not
remove for some reason
- `superfluous-else` eliminate more superfluous `else` branches

Rules are also sorted alphabetically and I cleaned up various parts of
`.golangci.yml`.

(cherry picked from commit 74f0c84fa4245a20ce6fb87dac1faf2aeeded2a2)

Conflicts:
	.golangci.yml
	apply the linter recommendations to Forgejo code as well

services/gitdiff/gitdiff.go

@@ -1040,8 +1040,8 @@ func createDiffFile(diff *Diff, line string) *DiffFile {
 			// diff --git a/b b/b b/b b/b b/b b/b
 			//
 			midpoint := (len(line) + len(cmdDiffHead) - 1) / 2
-			new, old := line[len(cmdDiffHead):midpoint], line[midpoint+1:]
-			if len(new) > 2 && len(old) > 2 && new[2:] == old[2:] {
+			newl, old := line[len(cmdDiffHead):midpoint], line[midpoint+1:]
+			if len(newl) > 2 && len(old) > 2 && newl[2:] == old[2:] {
 				curFile.OldName = old[2:]
 				curFile.Name = old[2:]
 			}