Improve ellipsize performance

Instead of iterate all ellipsized characters, only iterate the necessary
ranges for copying.

Bug: 188913943
Test: atest CtsTextTestCases CtsGraphicsTestCases CtsWidgetTestCases
Change-Id: I3d03b1e3897e427c23fbe51315f412c57a4ce9e9
(cherry picked from commit 2c6121f3)