ClangCodeModel: Work around clangd cursor issue

If the cursor is right before the "." in a member access expression,
clangd interprets it as belonging to the member instead of the base
expression, which leads to unexpected behavior.
Work around this by sending a cursor position one to the left of the
real one to clangd in such cases.

Change-Id: I429ee9189760ccb02d231acfcb94ab6cfde3cd8d
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/languageclient/client.h

@@ -248,6 +248,8 @@ private:
 
     virtual void handleDocumentClosed(TextEditor::TextDocument *) {}
     virtual void handleDocumentOpened(TextEditor::TextDocument *) {}
+    virtual QTextCursor adjustedCursorForHighlighting(const QTextCursor &cursor,
+                                                      TextEditor::TextDocument *doc);
 
     using ContentHandler = std::function<void(const QByteArray &, QTextCodec *, QString &,
                                               LanguageServerProtocol::ResponseHandlers,