This is a follow-up to https://github.com/go-gitea/gitea/pull/33097.
When linking a submodule at a commit in either the repo view, or a diff
when adding a new submodule, link to the tree view of that submodules
intead of the individual commit. This shows the user the full tree,
instead of the diff of the commit.
This makes the assumption that the tree for a given SHA is at
`<repo_url>/tree/<sha>`. This URL format is supported by both Github &
Gitlab, but not Gitea. To fix this, add a redirect from
`<username>/<repo>/tree/<ref>` to `<username>/<repo>/src/<ref>`, so that
Gitea can support this URL structure.
This adds links to submodules in diffs, similar to the existing link
when viewing a repo at a specific commit. It does this by expanding diff
parsing to recognize changes to submodules, and find the specific refs
that are added, deleted or changed.
Related #25888
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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
