refactor: decouple git.Repository(ctx) from git.Commit & git.Tree (#38464)

1. Storing "ctx" in a long-living object is wrong
2. Make the commit & tree cacheable (for the future performance
optimization)
3. Also fix some bad designs like `// FIXME: bad design, this field can
be nil if the commit is from "last commit cache"`

ref:
* #33893

modules/git/tree_entry_gogit.go

@@ -7,6 +7,8 @@
 package git
 
 import (
+	"context"
+
 	"github.com/go-git/go-git/v5/plumbing"
 	"github.com/go-git/go-git/v5/plumbing/filemode"
 	"github.com/go-git/go-git/v5/plumbing/object"
@@ -29,15 +31,15 @@ func (te *TreeEntry) toGogitTreeEntry() *object.TreeEntry {
 	}
 }
 
-// Size returns the size of the entry
-func (te *TreeEntry) Size() int64 {
+// GetSize returns the size of the entry
+func (te *TreeEntry) GetSize(ctx context.Context, gitRepo *Repository) int64 {
 	if te.IsDir() {
 		return 0
 	} else if te.sized {
 		return te.size
 	}
 
-	ptreeGogitTree, err := te.ptree.gogitTreeObject()
+	ptreeGogitTree, err := te.ptree.gogitTreeObject(gitRepo)
 	if err != nil {
 		return 0
 	}
@@ -52,10 +54,10 @@ func (te *TreeEntry) Size() int64 {
 }
 
 // Blob returns the blob object the entry
-func (te *TreeEntry) Blob() *Blob {
+func (te *TreeEntry) Blob(gitRepo *Repository) *Blob {
 	return &Blob{
 		ID:   te.ID,
-		repo: te.ptree.repo,
+		repo: gitRepo,
 		name: te.Name(),
 	}
 }