Add support for alternative CDN when downloading packages

Since the actual download URL is returned by the Thunderstore API as a
redirect, signal the API with a query parameter that an alternative CDN
is preferred.

Initial plan was that the download provider would take alternative CDN
flag as a constructor parameter. This didn't work in practice, since
the initialization is done in beforeCreate(), which doesn't seem to
support calling methods defined in UtilityMixin. So the method is now
called in created(), and provider's state is accessed via getter and
setter.

Refs TS-2003

src/components/mixins/UtilityMixin.vue

@@ -5,6 +5,7 @@ import Component from 'vue-class-component';
 import R2Error from '../../model/errors/R2Error';
 import GameManager from '../../model/game/GameManager';
 import Profile from '../../model/Profile';
+import ThunderstoreDownloaderProvider from '../../providers/ror2/downloading/ThunderstoreDownloaderProvider';
 import LoggerProvider, { LogSeverity } from '../../providers/ror2/logging/LoggerProvider';
 import ThunderstorePackages from '../../r2mm/data/ThunderstorePackages';
 import ProfileModList from '../../r2mm/mods/ProfileModList';
@@ -100,6 +101,7 @@ export default class UtilityMixin extends Vue {
             }
         }
 
+        ThunderstoreDownloaderProvider.instance.setUseAlternativeCdn(useAlt);
         this.$store.commit("setUseAlternativeCdn", useAlt);
     }
 }

src/providers/ror2/downloading/ThunderstoreDownloaderProvider.ts

@@ -10,6 +10,7 @@ import Game from '../../../model/game/Game';
 import Profile from '../../../model/Profile';
 
 export default abstract class ThunderstoreDownloaderProvider {
+    private useAlternativeCdn = false;
 
     private static provider: () => ThunderstoreDownloaderProvider;
     static provide(provided: () => ThunderstoreDownloaderProvider): void {
@@ -23,6 +24,14 @@ export default abstract class ThunderstoreDownloaderProvider {
         return ThunderstoreDownloaderProvider.provider();
     }
 
+    public getUseAlternativeCdn(): boolean {
+        return this.useAlternativeCdn;
+    }
+
+    public setUseAlternativeCdn(value: boolean) {
+        this.useAlternativeCdn = value;
+    }
+
     /**
      * Resolve all downloadable dependencies of a ThunderstoreVersion matching their exact version numbers.
      * This method is recursive to allow dependency building from nested dependencies.

src/r2mm/downloading/BetterThunderstoreDownloader.ts

@@ -288,7 +288,13 @@ export default class BetterThunderstoreDownloader extends ThunderstoreDownloader
             callback(100, StatusEnum.SUCCESS, null);
             return;
         }
-        axios.get(combo.getVersion().getDownloadUrl(), {
+
+        let downloadUrl = combo.getVersion().getDownloadUrl()
+        if (this.getUseAlternativeCdn()) {
+            downloadUrl += "?mirror=1";
+        }
+
+        axios.get(downloadUrl, {
             onDownloadProgress: progress => {
                 callback((progress.loaded / progress.total) * 100, StatusEnum.PENDING, null);
             },