Make media query classes GarbageCollected

To support calc() in media queries (and container queries), we need
to store a CSSValue in MediaQueryExpValue. This CL prepares for that.

Moving this to Oilpan is a little painful, since it means converting
certain objects from std::unique_ptr (less overhead) to
GarbageCollected (more overhead), but there is no other good option
as long as CSSValue is GarbageCollected.

Persistent is also not an option, because it would create a gc-root
inside already-GarbageCollected objects.

Bug: 1312000
Change-Id: I6f3baa317ffc69f2abbed0b8feab03817db0c4ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3683165
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1009985}