Adjust object format interface (#28469)

- Remove `ObjectFormatID`
- Remove function `ObjectFormatFromID`.
- Use `Sha1ObjectFormat` directly but not a pointer because it's an
empty struct.
- Store `ObjectFormatName` in `repository` struct

modules/git/object_id_test.go

@@ -10,7 +10,7 @@ import (
 )
 
 func TestIsValidSHAPattern(t *testing.T) {
-	h := NewSha1().Type()
+	h := Sha1ObjectFormat
 	assert.True(t, h.IsValid("fee1"))
 	assert.True(t, h.IsValid("abc000"))
 	assert.True(t, h.IsValid("9023902390239023902390239023902390239023"))