[cmake] Compile and run bitcoin-qt tests.

Summary: As per title.

Test Plan:
Run generated src/qt/test/test_bitcoin-qt manually. Checks it passes.
Run ninja check and ensures test_bitcoin-qt runs.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: jasonbcox, teamcity

Differential Revision: https://reviews.bitcoinabc.org/D1841