[Interop] Fix PointerEvent WPT for pointer-capture in iframe

The test is changed in 3 ways:

- All browsers are failing the 4th promise_test here [1] because
the test was wrongly making a pointer-capture request for the
`<iframe>` element on the top frame instead of an element inside
the iframe.  This is fixed.

- Removed the id `innerFrameElement` from all promise_tests to
avoid possible confusion along the same line.

- When the pointer-capture request is expected to fail, dragging
the pointer into or out-of an iframe activates a iframe-capture
behavior, probably on most browsers, that is not defined in the
PointerEvent spec.  Removed pointer dragging in these cases to keep
the tests focused on well-defined behaviors.

[1] https://wpt.fyi/results/pointerevents/pointerevent_pointercapture_in_frame.html%3Fmouse?label=experimental&label=master&aligned

Bug: 357041460
Change-Id: Ibda5890f5d7d2feb90868aa8e4e99a30ae51a180
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6150548
Commit-Queue: Mustaq Ahmed <mustaq@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Auto-Submit: Mustaq Ahmed <mustaq@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1404203}