* Prevent double sanitize.
* Use SanitizeReaderToWriter.
At the moment `actualRender` uses `SanitizeReader` to sanitize the output. But `SanitizeReader` gets called in `markup.render` too so the output gets sanitized twice.
I moved the `SanitizeReader` call into `RenderRaw` because this method does not use `markup.render`. I would like to remove the `RenderRaw`/`RenderRawString` methods too because they are only called from tests, the fuzzer and the `/markup/raw` api endpoint. This endpoint is not in use so I think we could remove them. If we really in the future need a method to render markdown without PostProcessing we could achieve this with a more flexible `renderer.NeedPostProcess` method.
* More efficiently parse shas for shaPostProcessor
The shaPostProcessor currently repeatedly calls git rev-parse --verify on both backends
which is fine if there is only one thing that matches a sha - however if there are
multiple things then this becomes wildly inefficient.
This PR provides functions for both backends which are much faster to use.
Fix #16092
* Add ShaExistCache to RenderContext
Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>
