For all manually-created images PNG have been kept.
- rename all icon attrs to have a `ic_` prefix
- always use `_24dp` icons, because there is no real difference, since they are vector drawables
- always use the original name found on material.io for icon drawables, as to not create confusion and possibly duplicates. Icon names can still be different from real drawable names, though I have made some of them compliant to this or maybe more meaningul.
- remove duplicate `getIconByAttr()` in ThemeHelper (use `resolveResourceIdFromAttr()`
- use standard icons for `expand_more` and `expand_less` instead of triangles
- use `play_button_outline` instead of custom PNG as play button in VideoDetailFragment (questionable, as there is no shadow anymore)
Changed android.R.string.ok, which is "OK", into R.string.finish, which is also OK, but from our strings
Then for a small amount of languages that don't have Android translation, it will show the good string.
renamed NewPipe's language into App language, and same for all the
concerning thing (keys, comments…)
we now call assureCorrectAppLanguage(CONTEXT) in activities needing it
instead of changeAppLanguage(getAppLocale(CONTEXT), RESOURCES)
changeAppLanguage becomes private.
* [DownloadDialog.java] use *.opus extension instead of *.webm (bad change from 844f80a5f1)
* [StreamItemAdapter.java] show "opus" in format label instead of "WebM Opus"
* restore permission request popup previously removed in #2486
* use legacy file picker in cases where saf file picker is not available
* fix missing file check logic in prepareSelectedDownload method (DownloadDialog.java)
* fix socket leak in "DownloadRunnable"
* in "DownloadInitializer" close the HTTP body after doing range-request checks
* in "DownloadRunnableFallback" fix typo in comment
* in "DownloadDialog" fix regression, using one thread for audios instead of subtitles
