This PR removes (almost) all path tricks, and introduces "renderhelper"
package.
Now we can clearly see the rendering behaviors for comment/file/wiki,
more details are in "renderhelper" tests.
Fix #31411 , fix #18592, fix #25632 and maybe more problems. (ps: fix
#32608 by the way)
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
