Due to the way emoji ZWJ sequences are defined, the ICU line breaking
algorithm determines that there are valid line breaks inside the
sequence. This patch suppresses these line breaks.

This is an adaptation of I225ebebc0f4186e4b8f48fee399c4a62b3f0218a
into the nyc-dev branch.

Bug: 25433289
Change-Id: I84b50b1e6ef13d436965eab389659d02a30d100f