Revert "Do not create 4-byte sequences in `ConvertUtf16ToModifiedUtf8()`"

This reverts commit e0a4f373dc4a738a2f26965a67d31239cbbd4f6a.

Reason for revert: DroidMonitor-triggered revert due to breakage https://android-build.googleplex.com/builds/tests/view?invocationId=I44000009917256156&testResultId=TR23027520914949881, bug b/193363191

Bug: 193363191
Change-Id: I2e7fe6de3f63864b58729d2c76e9ab5c95aa7983
15 files changed