Generate field-inject dispatch code

[mcculls]

What Does This Do

Adds build-time generation of the support bytecode needed for field-injected object-store dispatch:

• generates a synthetic KeyWithValue interface exposing indexed get/set accessors
• generates ObjectStoreDispatch, which uses injected accessors when available and falls back to GlobalObjectStore otherwise
• provides weakGet/weakPut entry points so an injected accessor can fall back without recursively re-entering dispatch
• preserves atomic getOrPut, getOrCompute, and remove behavior on the injected fast path with double-checked locking
• relocates the dispatch types and GlobalObjectStore implementation under java.lang.$Datadog$ and packs them as glue for future bootstrap-classpath injection
• strips annotations, generic signatures, and debug metadata from the relocated glue, and keeps the generated constant holder out of the published jar
• keeps GlobalObjectStore and ObjectStoreIds as package-private implementation details

Motivation

Field injection needs a fast path that stores values directly on instrumented key objects, while retaining the existing weak global store for keys that cannot be injected and for stores without an injected field.

This PR establishes the generated runtime types and bootstrap-safe fallback implementation needed for that dispatch. It is intentionally preparatory: it does not yet switch the public ObjectStore methods to the generated dispatcher or add the key-class transformation.

Additional Notes

Tests cover:

• structural and type-resolving verification of generated bytecode
• relocation of every Datadog-owned dependency needed by the bootstrap glue
• fast-path and fallback behavior for all dispatch operations
• fallback from an injected accessor without recursive dispatch
• single-winner behavior for concurrent getOrPut calls

Verified with:

./gradlew :field-inject:test

Contributor Checklist

Jira ticket: [PROJ-IDENT]

[amarziali]

looks good from my pov. I added a comment to understand better the implication of having different constraints on put wrt to things like getOrPut