Servo side of https://github.com/servo/stylo/pull/322.
Update the WPT expectation following the changes to make `::placeholder`
public and adding property restriction to `::placeholder` and
`::marker`. Additionally ensure that `getComputedStyle` works for
`::placeholder`.
Testing: Existing WPTs
Fixes: #43034Fixes: #43035Fixes: #19808
Signed-off-by: Jo Steven Novaryo <steven.novaryo@gmail.com>