gmlgo: Make `gmlgo generate` update assets with a `Uid`

[silbinarywolf]

Why?
I want to make gmlgo generate update assets with a Uid so that I can reference assets in non-code data files such as the room editor. This will allow me to rename asset names / identifiers without breaking room data.

Expectations

• It will also load all config.json files from each asset.
• If the file does not have a Uid, it will generate one.
• It will then make sure no Uid's are currently clashing. If they are, gmlgo will fail and inform the user that they need to fix the clashing issue manually. If two UIDs are clashing but one or both haven't been generated out to an actual file yet, it should try to regenerate and check for clashes again.