Improve diff file headers (#36215)

- reduce file name font size from 15px to 14px
- fix labels and buttons being cut off when their size is constrained
- change labels from monospace to sans-serif font
- move diff stats to right and change them from sum of changes to +/-
- change filemode to label and change text to match other labels

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/gitdiff/git_diff_tree.go

@@ -166,16 +166,6 @@ func parseGitDiffTreeLine(line string) (*DiffTreeRecord, error) {
 		return nil, fmt.Errorf("unparsable output for diff-tree --raw: `%s`, expected 5 space delimited values got %d)", line, len(fields))
 	}
 
-	baseMode, err := git.ParseEntryMode(fields[0])
-	if err != nil {
-		return nil, err
-	}
-
-	headMode, err := git.ParseEntryMode(fields[1])
-	if err != nil {
-		return nil, err
-	}
-
 	baseBlobID := fields[2]
 	headBlobID := fields[3]
 
@@ -201,8 +191,8 @@ func parseGitDiffTreeLine(line string) (*DiffTreeRecord, error) {
 	return &DiffTreeRecord{
 		Status:     status,
 		Score:      score,
-		BaseMode:   baseMode,
-		HeadMode:   headMode,
+		BaseMode:   git.ParseEntryMode(fields[0]),
+		HeadMode:   git.ParseEntryMode(fields[1]),
 		BaseBlobID: baseBlobID,
 		HeadBlobID: headBlobID,
 		BasePath:   basePath,