fix(lsp): skip widening for indexed source files (#2052)

Fixes #2034

Call hierarchy, Find Usages and rename widen a server's answer by opening project files that mention the symbol's name and asking again. For JDT LS those files are mostly sources it already analyses, so nearly every incoming-calls request ran a second, slow round before anything was shown. Widening now asks the server which candidates are already in its analysis scope (optional `openidea.workspace.coveredFiles` command, served by the bundled JDT extension using the live source search scope) and only opens the rest; a missing or failing answer keeps the previous behaviour. Covers call hierarchy, references and rename. Hierarchy on a multi-module Maven fixture: median 703 ms → 224 ms, one query round.

java/java-usages/plugin.xml

@@ -1,6 +1,9 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <plugin>
   <extension point="org.eclipse.jdt.ls.core.delegateCommandHandler">
+    <delegateCommandHandler class="ai.openidea.usages.CoveredFilesCommand">
+      <command id="openidea.workspace.coveredFiles"/>
+    </delegateCommandHandler>
     <delegateCommandHandler class="ai.openidea.usages.UsagesCommand">
       <command id="openidea.java.usages"/>
     </delegateCommandHandler>