Implement subpage generation

[dplochcoder]

Summary of Changes

• Fixes menu screen titles not supporting l10n
• Implements subpage generation
  • Can be done automatically through config structure, through custom attributes, or via extending ConfigEntryFactory with custom behavior. Subpage generation is opt-in and requires interested plugins to implement the IModMenuNestedMenu interface to get it.
• Other minor maintenance not generally user-visible.

This is a breaking change, but only for mods that create their own custom menus (auto-gen is unaffected), and so should be released with an accompanying notification on the mod server. Like the last l10n update, the breakage is mostly source-compatible, but it does require rebuilds and it does require changing implementations of string ModMenuName() to LocalizedText ModMenuName(). I'm not aware of any other breaking changes needed for l10n or otherwise at this time.

Checklist

• No change is too small for a release, so pick one:
  • I have updated the package version following semantic versioning
  • There is another change actively WIP that will update the version (link issue or PR here)
  • This PR does not update user-facing code/config
  • I'm not sure how to set the version and would like the reviewer's help

[flibber-hk]

I am sure something weird is going on here - I have ostensibly selected option 5 but option 4 still has the L/R fleurs. I'm 99% sure this is out of scope for this PR but just checking if you know anything about it

EDIT Most likely this is because the fleurs aren't getting animated with the MenuOptionHorizontal removed - I'd guess the correct fix is to animate them explicitly (similar to the description). I'm gonna create a new issue

[flibber-hk]

Approval subject to the unresolved comments (although some of them may not require action :zotesip:)

[flibber-hk]

Um, what is the intended behaviour if you do

        Config.Bind(new("Main.B.C", "Int7"), 7, new("ABC Integer 7"));
        Config.Bind(new("Main.B.C", "Int8"), 8, new("ABC Integer 8"));

What happens is that both of these get placed on the main page

[dplochcoder]

Um, what is the intended behaviour if you do

        Config.Bind(new("Main.B.C", "Int7"), 7, new("ABC Integer 7"));
        Config.Bind(new("Main.B.C", "Int8"), 8, new("ABC Integer 8"));

What happens is that both of these get placed on the main page

This was not intended, fixed the algorithm so that it handles the "Main.B.C" collapse correctly.