This is only used for CSS style sheets. One case wants it as a String,
and the others don't care, but will in future also want to have the
source as a String.
(cherry picked from commit 8cbc2116162764479edeec78e4b2b7c41447b643;
amended to fix conflicts in two cmake files, due to serenity
still having more code_generators, and still buildling
OutOfProcessWebView.cpp. Also kept embed_as_string_view because
it's used by stringify_gml. Did this by giving embed_as_string.py
a --type= argument that defaults to string but can also be set
to string-view.)
