layout: Have `TextRun::glyph_run_is_preserved_newline` take into account `TextRunSegment` offset (#32119)

A `TextRun` is composed of `TextRunSegment`s that are composed of
`GlyphRun`s.
`TextRun::glyph_run_is_preserved_newline` is indexing into the `TextRun`
text, but the `GlyphRun` indexes that it uses are relative to the
`TextRunSegment`
offset. Before the code was using the offset without incorporating the
`TextRunSegment` offset. This led to miscalculation of preserved newline
location while processing text content.

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