Find in document — test build for PR #579

Test build for GrapheneOS/PdfViewer#579 — find in document.

This is a debug build, signed with a throwaway debug key. It installs alongside a release
install as PDF Viewer d (app.grapheneos.pdfviewer.debug). It is for trying the PR out, not for
general use — install the real app from GrapheneOS for that.

Trying it

1. Install the APK and open any PDF with it.
2. Tap the magnifier in the toolbar.
3. Type. Results appear as the document is indexed; the progress bar shows how far the sweep has
   got, and the count carries a + until it finishes.
4. Up/down step through matches and wrap around the document. Back closes the find bar.

Worth trying: a word that occurs hundreds of times, an accented or ligatured word searched without
the accent (resume finds Résumé, fi finds fi), a phrase that spans a line break, zooming and
rotating with matches on screen, and a document large enough to watch the progress bar move.

Built from the search branch at the commit referenced in the PR.