fix(java): stop Show Usages waiting seconds on the configuration index after a change (#2011)

Usages counts clicked after a Java change waited for the configuration index to resolve every dependency's Spring metadata again (15–20 s in a Spring Boot project). The Java extension (1.8.0) now keeps each dependency JAR's metadata across rebuilds until the JAR or the classpath changes, and Show Usages shows the Java usages first, adding the configuration ones when the index takes longer.

Closes #1898

java/java-usages/tests/configuration.py

@@ -244,6 +244,14 @@ try:
     while not query('added.size')['locations']:
         assert time.monotonic() < deadline, 'a new source on disk did not reach the index'
         time.sleep(0.2)
+    # That rebuild reused the library's metadata; a changed archive is read again.
+    assert query('vendor.port')['locations'], 'a source rebuild lost the library metadata'
+    metadata['properties'].append({'name': 'vendor.speed', 'type': 'java.lang.Integer', 'sourceType': 'vendor.LibrarySettings'})
+    with zipfile.ZipFile(library, 'w') as z:
+        z.write(classes / 'vendor/LibrarySettings.class', 'vendor/LibrarySettings.class')
+        z.writestr('META-INF/spring-configuration-metadata.json', json.dumps(metadata))
+    assert query('vendor.speed')['locations'], 'a changed library archive kept its old metadata'
+    assert query('vendor.port')['locations']
     # Unsaved changes must replace old keys, and closing must restore disk keys.
     changed = source.replace('prefix="app"', 'prefix="edited"').replace('${app.time-out:30}', '${edited.timeout:30}')
     send({'jsonrpc': '2.0', 'method': 'textDocument/didChange', 'params': {'textDocument': {'uri': file.as_uri(), 'version': 2}, 'contentChanges': [{'text': changed}]}})