[Issue #1348] Support New Code Search and Code View feature preview

- Added initial support for [New Code Search and Code View feature preview](https://docs.github.com/en/repositories/working-with-files/managing-files/navigating-files-with-the-new-code-view): * All text on Code pane * Symbol name on Symbols pane  Related issue: https://github.com/StylishThemes/GitHub-Dark/issues/1348