Improve QrCodeGenerator.encodeQrCode performance

Call Bitmap.setPixels() once instead of setPixel() multiple times.

Bug: 304560734
Test: manual - on "About phone" page
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:f8d17833044de41ea37547758b79a41f6fcf5370)
Merged-In: I6e1be2e394764c3bb19db23f18070f71b80c31e7
Change-Id: I6e1be2e394764c3bb19db23f18070f71b80c31e7