Bug 52760

Consider a run of 2 characters where each is in its own CTRun. As the ComplexTextRuns are iterated by ComplexTextController::advance(), glyphStartOffset gets 0, but glyphEndOffset gets 2 via complexTextRun.stringLength(), which results in a width of half the first adjusted advance: half because it is divided equally among 2 characters, and no more since"glyphEndOffset + complexTextRun.stringLocation() > m_currentCharacter" is true, which causes the loop to exit. In order to fix this, ComplexTextRun needs to keep track of the original run range in order to return the end index (end in the sense of an STL range, or one past the last included value). Note that the string indices alone are not sufficient to determine the end index, as the last glyph may be a ligature and subsume more than one index.