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
- When pasting a URL over another URL, replace the URL instead of
creating a useless `[url](url)`. This is the 1-line change
[here](https://github.com/go-gitea/gitea/pull/31948/files#diff-be8e94d7e3da33b187381f53d28095107bd0cf29ae9a9e997e4f422f4a54479cR122).
- Always run `initTextareaEvents`, previously it was not run when
`dropzoneEl` was not present like when attachements are disabled on the
server. Refactored the function to gracefully handle absent `dropzoneEl`
and rename the function to a better name.
None of the frontend js/ts files was touched besides these two commands
(edit: no longer true, I touched one file in
61105d0618
because of a deprecation that was not showing before the rename).
`tsc` currently reports 778 errors, so I have disabled it in CI as
planned.
Everything appears to work fine.
