Make list of subterms in debug output easier to spot

Summary:
'(' was used for both delimiting Terms and list of Subterms. Use '[' for
lists instead.
Old:
( AND ( : a (QString)) ( AND ( OR ( : b (QString)) ( : c (QString)) ) ( : d (QString)) ) )
New:
[ AND ( : a (QString)) [ AND [ OR ( : b (QString)) ( : c (QString)) ] ( : d (QString)) ] ]

Test Plan: ctest -V

Reviewers: Baloo, michaelh

Reviewed By: Baloo, michaelh

Subscribers: Frameworks

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D12006