Set up empty lines for DynamicLayout#updateBlocks() tests

The changes in I666da5eeb39f780c341597f347bfcba21eb34295 introduced
the concept of lines that need to be always redrawn, but it broke
tests for DynamicLayout#updateBlocks() that didn't need to set up the
actual lines.

Now, during the test setup, we insert empty lines to match the number
of lines needed.

Test: adb shell am instrument -w -e class android.text.DynamicLayoutBlocksTest com.android.frameworks.coretests/android.support.test.runner.AndroidJUnitRunner
Test: adb shell am instrument -w -e class android.text.DynamicLayoutTest#testGetBlocksAlwaysNeedToBeRedrawn_thai com.android.frameworks.coretests/android.support.test.runner.AndroidJUnitRunner
Test: adb shell am instrument -w -e class android.text.DynamicLayoutTest#testGetBlocksAlwaysNeedToBeRedrawn_en com.android.frameworks.coretests/android.support.test.runner.AndroidJUnitRunner
Test: cts-tradefed run cts-dev --module CtsTextTestCases
Change-Id: I4bfc82db4beef1b740433a25a3ae29201f54d9d3
Fixes: 38029583