ClangCodeModel: Provide tooltips via clangd

Note that we temporarily lose the ability to hover over an include and
get the full path of the header file. This is a valuable feature that we
need to restore, preferably by fixing clangd itself.
Fixing the remaining few test failures would likely require more
complicated code as well as additional LSP round-trips, and as of now
I'm not convinced it is worth the effort.

Change-Id: I08c72c4bd1268bbd67baeb57bbfd29d9b11303a5
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/clangcodemodel/clangcodemodelplugin.cpp

@@ -208,6 +208,7 @@ QVector<QObject *> ClangCodeModelPlugin::createTestObjects() const
         new Tests::ClangdTestFindReferences,
         new Tests::ClangdTestFollowSymbol,
         new Tests::ClangdTestLocalReferences,
+        new Tests::ClangdTestTooltips,
     };
 }
 #endif