feat: add modrinth pack downloading

Things that don't work / work poorly (there's more for sure but those
are the evident ones):
    - Icons are broken in the import dialog
    - No way to search for private packs
    - Icons are not downloaded when downloading a mod
    - No support for multiple download URLs
    - Probably a lot more...

launcher/modplatform/modrinth/ModrinthPackManifest.cpp

@@ -14,3 +14,87 @@
  */
 
 #include "ModrinthPackManifest.h"
+#include "Json.h"
+
+#include "minecraft/MinecraftInstance.h"
+#include "minecraft/PackProfile.h"
+
+namespace Modrinth {
+
+void loadIndexedPack(Modpack& pack, QJsonObject& obj)
+{
+    pack.id = Json::ensureString(obj, "project_id");
+
+    pack.name = Json::ensureString(obj, "title");
+    pack.description = Json::ensureString(obj, "description");
+    pack.authors << Json::ensureString(obj, "author");
+    pack.iconName = QString("modrinth_%1").arg(Json::ensureString(obj, "slug"));
+    pack.iconUrl = Json::ensureString(obj, "icon_url");
+}
+
+void loadIndexedInfo(Modpack& pack, QJsonObject& obj)
+{
+    pack.extra.body = Json::ensureString(obj, "body");
+    pack.extra.sourceUrl = Json::ensureString(obj, "source_url");
+    pack.extra.wikiUrl = Json::ensureString(obj, "wiki_url");
+
+    pack.extraInfoLoaded = true;
+}
+
+void loadIndexedVersions(Modpack& pack, QJsonDocument& doc)
+{
+    QVector<ModpackVersion> unsortedVersions;
+
+    auto arr = Json::requireArray(doc);
+
+    for (auto versionIter : arr) {
+        auto obj = Json::requireObject(versionIter);
+        auto file = loadIndexedVersion(obj);
+
+        if(!file.id.isEmpty()) // Heuristic to check if the returned value is valid
+            unsortedVersions.append(file);
+    }
+    auto orderSortPredicate = [](const ModpackVersion& a, const ModpackVersion& b) -> bool {
+        // dates are in RFC 3339 format
+        return a.date > b.date;
+    };
+
+    std::sort(unsortedVersions.begin(), unsortedVersions.end(), orderSortPredicate);
+
+    pack.versions.swap(unsortedVersions);
+
+    pack.versionsLoaded = true;
+}
+
+auto loadIndexedVersion(QJsonObject &obj) -> ModpackVersion
+{
+    ModpackVersion file;
+
+    file.name = Json::requireString(obj, "name");
+    file.version = Json::requireString(obj, "version_number");
+
+    file.id = Json::requireString(obj, "id");
+    file.project_id = Json::requireString(obj, "project_id");
+    
+    file.date = Json::requireString(obj, "date_published");
+
+    auto files = Json::requireArray(obj, "files");
+
+    for (auto file_iter : files) {
+        File indexed_file;
+        auto parent = Json::requireObject(file_iter);
+        if (!Json::ensureBoolean(parent, "primary", false)) {
+            continue;
+        }
+
+        file.download_url = Json::requireString(parent, "url");
+        break;
+    }
+
+    if(file.download_url.isEmpty())
+        return {};
+
+    return file;
+}        
+
+}  // namespace Modrinth