Import keys from filesystem. (#13056)

* Import keys, re-initialize KeyManager, re-scan vfs, re-populate game list.

* <.< spelling.

* Update based on feedback on #13047 and this PR

* Based on feedback: Don't delete existing files. There's legitimate reasons that someone may want to keep their retail keys and title key handling is resilient to mismatches.

* Update src/yuzu/main.cpp

Co-authored-by: Tobias <thm.frey@gmail.com>

* Remove translation of literal filename/filter format.

* clang-format.

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Co-authored-by: Tobias <thm.frey@gmail.com>

src/yuzu/main.h

@@ -381,6 +381,7 @@ private slots:
     void OnOpenYuzuFolder();
     void OnVerifyInstalledContents();
     void OnInstallFirmware();
+    void OnInstallDecryptionKeys();
     void OnAbout();
     void OnToggleFilterBar();
     void OnToggleStatusBar();