LanguageClient: Add the possibility to override progress messages

... and make use of it in the clangd client.
We want the progress bar for background indexing to have a better title
than the plain (and non-translated) "indexing" that the clangd server
sends.

Change-Id: Ib75eac370e7c22f0c5bd477f4a4c423283b27e1f
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangcodemodel/clangdclient.cpp

@@ -63,6 +63,7 @@ ClangdClient::ClangdClient(ProjectExplorer::Project *project, const Utils::FileP
     setClientCapabilities(caps);
     setLocatorsEnabled(false);
     setDocumentActionsEnabled(false);
+    setProgressTitleForToken("backgroundIndexProgress", tr("Parsing C/C++ Files (clangd)"));
     setCurrentProject(project);
     start();
 }