It is possible to pass in objects that are not trusted scripts into the
Function constructor. Rather than crashing, we now treat these as
untrusted. `can_compile_string_with_trusted_type` doesn't need to know
the contents of a string, as it always marks it as untrusted.
We can make the same optimization in the string case, where we no longer
need to convert the string.
Testing: This change adds a WPT crash test.
Fixes#39436
Signed-off-by: Tim van der Lippe <tvanderlippe@gmail.com>