Begin to Document Script Data

[ravepossum]

This PR:

• Begins to document the structure used to store script data (currently named ScriptManager) and a lot of the related functionality.
• Adds a new constgen file for script commands, scrcmd.json
• Documents a couple script commands, CheckSaveType and ScrollBG3

Remaining items (in general, not necessarily for this PR):

• Documenting the rest of the ScriptManager struct (there's a few struct members that aren't documented). Both the struct itself, and the enumeration used in the accessor ScriptManager_GetMemberPtr.
• Creating preproc constants for the rest of the script ID offsets
• Documenting the remainder of the functions in unk_0203E880.c
• Renaming unk_0203E880

[ravepossum]

Everything should be addressed + the files have been renamed now.

[cbt6]

LGTM