[GeometryInterface] add transformPoint(point) function.

Let point object be the result of invoking create
a DOMPoint from the dictionary point.
Point object is post-multiplied to the current matrix
and returns the resulting point.
The passed argument does not get modified.

spec list:
https://drafts.fxtf.org/geometry/#dom-dommatrixreadonly-transformpoint

BUG=388780

Review-Url: https://codereview.chromium.org/2423753002
Cr-Commit-Position: refs/heads/master@{#432762}
6 files changed