feat(web): optimization via lazy construction of OSK layers ⏩

[jahorton]

Continues from #11263, addressing part of #11166.

One particularly easy way to load and display the OSK more quickly is to simply... not make the parts you don't need yet. We can do just-in-time (JIT) construction of OSK layers when they're needed.

While the default layer is pretty much always needed, and some keyboards will sometimes start in one or two other layers... a large number of keyboards have extra layers that can wait.

As there's one more followup on this set of PRs...

@keymanapp-test-bot skip

[keymanapp-test-bot[bot]]

User Test Results

Test specification and instructions

User tests are not required

Test Artifacts

• Android
  • Keyman for Android apk
  • FirstVoices for Android 16.0 apk
  • FirstVoices Keyboards for Android apk
  • KeyboardHarness apk
  • Keyman for Android 16.0 apk
  • KMSample1 apk
  • KMSample2 apk
• Developer
  • Keyman Developer - build failure
  • Compiler Regression Tests - build failure
  • kmcomp.zip - build failure
• iOS
  • Keyman for iOS (simulator image)
  • FirstVoices Keyboards for iOS (simulator image)
  • TestFlight internal PR build version - 18.0.21 (0.11264.10806)
• Keyboards
  • Test Keyboards - build failure
• Web
  • KeymanWeb Test Home
• Windows
  • Keyman for Windows - build failure
  • FirstVoices Keyboards for Windows - build failure
  • Text Editor (32 bit) - build failure
  • Text Editor (64 bit) - build failure

[jahorton]

Current build-failure cause:

15:26:42   renderer_core.ts(181,54): error TS2341: Property 'layers' is private and only accessible within class 'OSKLayerGroup'.

Right, some of the tools will want access to that.