citra-qt: Add an "Alternative Speed Limit" with its hotkey (#5281)

* Change "Toggle Speed Limit" to toggle between 100% and a custom value

This will change the shortcut for "Toggle Speed Limit" to make it swap between 100% and the value of "Limit Speed Percent" in the config. Old functionality is still there, but renamed to "Unthrottle".

* Complete reimplementation of the function

* Fix something that didn't get saved correctly

* Fix missing indentation

* Rewrite to keep only a single QSpinBox

* Second rewrite

* set Unthrottled to 0 in the Qspinbox

* Hotkey for Unthrottle

* minor improvements to the design

* Apply suggestions from code review

Co-authored-by: Ben <bene_thomas@web.de>

* Default slider values

* clang-format fixes

* Prevent the speed slider from changing size

...when an element in its row has variable width.

* Change "Game Speed" to "Emulation Speed"

* Apply suggestions from code review

`game_speed` to` emulation_speed`

Co-authored-by: Valentin Vanelslande <vvanelslandedev@gmail.com>

* Fix for QSliders

* Revert "Prevent the speed slider from changing size"

This reverts commit ddaca20044.

* clang-format

...doesn't seem to stick to a choice

* Fix 2 for QSliders

Co-authored-by: B3n30 <benediktthomas@gmail.com>
Co-authored-by: Ben <bene_thomas@web.de>
Co-authored-by: Valentin Vanelslande <vvanelslandedev@gmail.com>

src/core/settings.h

@@ -155,8 +155,9 @@ struct Values {
     bool shaders_accurate_mul;
     bool use_shader_jit;
     u16 resolution_factor;
-    bool use_frame_limit;
+    bool use_frame_limit_alternate;
     u16 frame_limit;
+    u16 frame_limit_alternate;
     std::string texture_filter_name;
 
     LayoutOption layout_option;