fix: utilize APP_NAME in prepare_vscode.sh

[rizese]

Hi! While playing around with building, I noticed changing the APP_NAME in the build/build.sh script didn't actually change the name of the final executable and its bundles. So - here's a fix 👍

This is tested ONLY in macOS

[daiyam]

Some of those APP_NAME are vscodium or codium.

For a fork, updateUrl, downloadUrl and lot of others place need to be customized. Here, how I do it: https://github.com/zokugun/MrCode/blob/master/prepare.sh

The final naming of the executables are done in https://github.com/VSCodium/vscodium/blob/master/prepare_assets.sh It's executed with ./build/build.sh -p

[rizese]

Thanks @daiyam !