refactor: Move icons into light/dark folders

This follows the vscode styles where all icons for dark mode are in
the `dark` folder and all for light mode in the `light` folder. They
always have the same name.

extensions/ql-vscode/package.json

@@ -178,8 +178,8 @@
         "command": "codeQL.chooseDatabase",
         "title": "CodeQL: Choose Database",
         "icon": {
-          "light": "media/black-plus.svg",
-          "dark": "media/white-plus.svg"
+          "light": "media/light/plus.svg",
+          "dark": "media/dark/plus.svg"
         }
       },
       {

extensions/ql-vscode/src/databases-ui.ts

@@ -15,8 +15,8 @@ type ThemableIconPath = { light: string; dark: string } | string;
  * Path to icons to display next to currently selected database.
  */
 const SELECTED_DATABASE_ICON: ThemableIconPath = {
-  light: 'media/check-light-mode.svg',
-  dark: 'media/check-dark-mode.svg',
+  light: 'media/light/check.svg',
+  dark: 'media/dark/check.svg',
 };
 
 /**