ecode: add configurable screenshot support

Add an unlocked take-screenshot command and expose it under Settings -> Window with a default Print Screen binding.

Allow configuring the screenshot destination, filename pattern, and output format. Save screenshots under the ecode configuration directory by default, notify users after capture, and provide an action to open the result in the integrated image viewer.

Addresses a request in SpartanJ/ecode#950.

src/tools/ecode/settingsactions.hpp

@@ -40,6 +40,12 @@ class SettingsActions {
 
 	void setUIPanelFontSize();
 
+	void setScreenshotSavePath();
+
+	void setScreenshotFilenamePattern();
+
+	void setScreenshotSaveFormat();
+
   private:
 	App* mApp{ nullptr };