perf(java): keep the configuration snapshot across editor activity

The configuration index was invalidated by every Java element event,
including POST_RECONCILE, and its working-copy fingerprint covered every
open editor. Opening the navigation target, closing a tab, or saving
application.yml was enough to make the next Find Usages or YAML key
navigation rebuild the whole project index.

Invalidation now follows what the index depends on:
- POST_CHANGE deltas only, ignoring working-copy open/close, AST-only
  flags and non-Java resource content on projects, roots and packages
  (configuration files are parsed by the client, metadata files are
  stamp-checked).
- The fingerprint covers working copies with unsaved changes only.

Each snapshot reports a generation so the real-server harness can assert
that opening/closing editors, a full build and a saved edit keep it warm,
while a source added on disk still invalidates it.

Bundle 1.2.1 (installed as java-usages-1.2.1.jar so OSGi does not reuse
the cached 1.2.0), reproducible SHA-256
cbae3e3a0bcf2818b4cc9d98998bd9b81f92e1ae7803dc757134485f9776a4e1.

plugins/java-usages/README.md

@@ -57,7 +57,7 @@ is not a claim of full IntelliJ feature parity.
 ## Rebuild and delivery
 
 The checked-in jar is embedded by ide-sdk `include_bytes!`, installed as
-`java-usages-1.2.0.jar`, and added alongside existing initialization bundles.
+`java-usages-1.2.1.jar`, and added alongside existing initialization bundles.
 Users need no compiler, Maven or Python. Manifest/install version must change
 when replacing the bundle because OSGi caches bundles.
 
@@ -70,6 +70,9 @@ and compare SHA-256. The prior 1.1.1 output was
 `1e569939cba22c7db6e2c9b53de2a4c10ccaabe762a51427119a04af3d974ae4`.
 Version 1.2.0 adds the configuration command; its reproducible SHA-256 is
 `9140f1d2ecf27eadfe66b40a17daa18a08a65927ebef79456ba55d486ce5eeba`.
+Version 1.2.1 keeps the configuration snapshot across editor open/close, saves of
+unrelated content and non-Java resource changes; its reproducible SHA-256 is
+`cbae3e3a0bcf2818b4cc9d98998bd9b81f92e1ae7803dc757134485f9776a4e1`.
 
 ```sh
 export PATH=/path/to/jdk25/bin:$PATH