Fix syntax support for dynamic member access.

Covers syntax like:
- A::${$foo}
- A::$var::${$foo}
- A::$var->${$foo}

BUG: 400294
FIXED-IN: 5.3.1

Reviewers: kfunk

Reviewed By: kfunk

Subscribers: kfunk, kdevelop-devel

Tags: #kdevelop

Differential Revision: https://phabricator.kde.org/D16461