mobile: app: Fix TableOfContents

Summary:

• Correct QQC2 import
• Apply search field changes from Thumbnails here as well

Test Plan:

• Open https://openboard.ch/download/Tutoriel_OpenBoard_1.5EN.pdf with okularkirigami
• open the context drawer
• switch to the "Table of Contents" tab
• the ToC should load successfully

Reviewers: Okular, bshah

Reviewed By: bshah

Subscribers: bshah, okular-devel

Tags: Okular

Differential Revision: https://phabricator.kde.org/D23066