Add full support for GameTest Exports

[Mickey42302]

After doing some coding, I got the export sub-commands for "/test" working, as well as the SNBT functionality for "/place template". A number of changes were needed since Mojang overhauled the feature despite it being unavailable by default.

To improve consistency, I gave the export utilities their own configuration option ("register-minecraft-export-commands"). The "register-minecraft-debug-commands" configuration option controls the commands which can also be registered using the "MC_DEBUG_DEV_COMMANDS" debug property.

The "Export Structure" button in Test Instance Blocks works as well. Please note that this button is only available if you have my development tools patch installed on your client (https://github.com/Mickey42302/JavaEditionDevTools).

Accepting this pull request will close issue #1716 as well.

[granny]

Please review the following comment in your previous PR and use that information to improve the maintainability of this PR. #1729 (review)

[Mickey42302]

I've converted the feature patches to file patches.

[granny]

I've gone through the effort of making this PR more maintainer-friendly. As I was fixing it up, I started having this feeling that this implementation feels more hacky than I'd like it to be. Will come back to this PR at a later date.

[Mickey42302]

I understand. I tried my best with the patches. Mojang overhauled the code, so enabling the export tools is no longer as simple as overriding some values/if statements.

I do wonder why Mojang is keeping this feature hidden from the public, though. It could be very useful for content creators.