Issue 708 - Needed the search for external references to occur in a r…

…ead action. I'm unfortunately unable to reproduce the actual error seen by the reporting user in 2023.2 or 2024.3, but wrapping the entire call in a read action should resolve all downstream requirements for the read lock.

src/main/java/com/redhat/devtools/lsp4ij/usages/LSPUsageSearcher.java

@@ -98,7 +98,11 @@ public void processElementUsages(@NotNull PsiElement element, @NotNull Processor
         }
 
         // For completeness' sake, also collect external usages to LSP (pseudo-)elements
-        LSPExternalReferencesFinder.processExternalReferences(file, element.getTextOffset(), reference -> processor.process(new UsageInfo2UsageAdapter(new UsageInfo(reference))));
+        ReadAction.run(() -> LSPExternalReferencesFinder.processExternalReferences(
+                file,
+                element.getTextOffset(),
+                reference -> processor.process(new UsageInfo2UsageAdapter(new UsageInfo(reference)))
+        ));
     }
 
     @Nullable