Fix 26.3 block-state provider backporting to 26.2

[lukasbeppi]

Minecraft 26.2 clients can fail during registry loading with Unknown registry key ... minecraft:worldgen/block_state_provider_type: minecraft:simple when Frost Walker contains a 26.3 block-state provider. This was observed with ViaFabricPlus 5.0.2 and its bundled ViaBackwards 5.12.0; the provider conversion is still unchanged on current master. The enchantment condition fixes from #1346 do not cover this case.

Minimal failing provider:

{type:"simple",state:{id:"minecraft:frosted_ice",properties:{age:"0"}}}

This restores all eight renamed vanilla provider identifiers and their pre-26.3 block-state representation, including weighted/noise state lists and nested providers. The superclass runs before the conversion so its block mappings still see the 26.3 fields. Already converted states retain their Name and properties, and unrelated provider namespaces remain unchanged. Existing enchantment condition handling is preserved.

Validation:

• The unmodified current master reproduces the original Frost Walker codec failure. The corrected provider is accepted by the actual Minecraft 26.2 codec.
• An external regression harness passed 40 assertions against the built common module and the project's declared ViaVersion dependency. These cover the complete enchantment rewrite, all eight provider names, nested providers, state properties, weighted entries, noise lists, existing/custom data, and repeated conversion.
• The complete Gradle build passed (./gradlew build). The repository currently has no test sources; the codec/regression checks above were run separately.

An actual in-game join with the modified build has not yet been confirmed. This contribution was prepared with AI assistance and checked locally.