fix(java): stop Show Usages waiting seconds on the configuration index after a change

After any Java change, the configuration index was rebuilt from scratch on the next Show
Usages, resolving every dependency's Spring metadata (thousands of Spring Boot properties)
to library members again, and Show Usages waited for it: 15-20 seconds in a Spring Boot +
MyBatis project.

- The Java extension (1.8.0) keeps each dependency JAR's metadata entries across rebuilds
  until the JAR's timestamp/size or the project's classpath changes.
- Show Usages shows the Java usages as soon as they are found and adds the configuration
  ones when the index takes longer.

Closes #1898

java/java-usages/README.md

@@ -69,7 +69,7 @@ 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-1.7.0.jar`, and added alongside existing initialization bundles.
+`java-usages-1.8.0.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.
 
@@ -103,6 +103,10 @@ Version 1.7.0 adds the `"sources"` scope to `openidea.java.usages`, searches eac
 file's decompiled source on its own and returns the line (`text`) of each usage in a library
 class; its reproducible SHA-256 is
 `56d35619d5be937b028ac143ba748365a66a74c803bc112e4788a7dce98b44fc`.
+Version 1.8.0 keeps each dependency JAR's configuration metadata across rebuilds of the
+configuration index (until the JAR or the project's classpath changes), so a source change no
+longer resolves every Spring Boot property again; its reproducible SHA-256 is
+`728ab33b5e01fa5e496818f25ddbc487458a92339026899b0e22abda5adfd67b`.
 
 ```sh
 export PATH=/path/to/jdk25/bin:$PATH