Add wasm-threaded configuration in 'dev' (and later Qt 6.5) packages

After https://codereview.qt-project.org/c/qt/qt5/+/442856 we already get wasm-threaded packages from macOS from 'dev' branch.

We need to add these packages in the installer as well, side by side existing wasm configuration.

• The item name in the installer UI will be: WebAssembly (multi-threaded)
• Description: >Qt %QT_VERSION% Prebuilt Components for WebAssembly (multi-threaded).

At the same time let's change the item name and description for existing webassembly item:

• The new item name in the installer UI will be: WebAssembly (single-threaded)
• Description: >Qt %QT_VERSION% Prebuilt Components for WebAssembly (single-threaded).