There were too many patches to the Render system, it's really difficult
to make further improvements.
This PR clears the legacy problems and fix TODOs.
1. Rename `RenderContext.Type` to `RenderContext.MarkupType` to clarify
its usage.
2. Use `ContentMode` to replace `meta["mode"]` and `IsWiki`, to clarify
the rendering behaviors.
3. Use "wiki" mode instead of "mode=gfm + wiki=true"
4. Merge `renderByType` and `renderByFile`
5. Add more comments
----
The problem of "mode=document": in many cases it is not set, so many
non-comment places use comment's hard line break incorrectly
Fixes: https://github.com/go-gitea/gitea/issues/30512
I think this does mean those tools would run on a potential `vendor`
directory, but I'm not sure we really support vendoring of dependencies
anymore.
`release` has a `vendor` prerequisite so likely the source tarballs
contain vendor files?
None of the features of `unrolled/render` package is used.
The Golang builtin "html/template" just works well. Then we can improve
our HTML render to resolve the "$.root.locale.Tr" problem as much as
possible.
Next step: we can have a template render pool (by Clone), then we can
inject global functions with dynamic context to every `Execute` calls.
Then we can use `{{Locale.Tr ....}}` directly in all templates , no need
to pass the `$.root.locale` again and again.
Replace #23350.
Refactor `setting.Database.UseMySQL` to
`setting.Database.Type.IsMySQL()`.
To avoid mismatching between `Type` and `UseXXX`.
This refactor can fix the bug mentioned in #23350, so it should be
backported.
