Conditionally snap the decoration line geometry

For text decorations on SVG text we don't want to snap the position of
them because that may produce poor results in some cases. We already
don't round the thickness of the decoration line.

In DecorationLinePainter::DrawLineForText() only call SnapYAxis()
conditionally based on if a cc::PaintFlags is passed - which currently
mean that SVG text is being painted. Other decoration styles than solid
are not supported yet on SVG text.

Bug: 40887872
Change-Id: I420da536c6bb81ddec481e5effbf32a65163c14e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5335369
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1267946}