[cssom-view] Change document.caretPositionFromPoint's shadowRoots parameter from rest parameter to a dictionary with an array of shadow roots

[siliu1]

Per issue #10345, We should change the API signature from document.caretPositionFromPoint(double x, double y, ShadowRoot... shadowRoots) to document.caretPositionFromPoint(double x, double y, optional CaretPositionFromPointOptions options = {}) where CaretPositionFromPointOptions is defined as:

dictionary CaretPositionFromPointOptions {
  sequence<ShadowRoot> shadowRoots = [];
};

[siliu1]

@zcorpan Please take a look. Thank you.

[siliu1]

@emilio Please take a look. Thank you!