Previously: CSSImportRule::loaded_style_sheet() (and others) depend on
the definition of class CSSStyleSheet. Meanwhile,
CSSStyleSheet::template for_each_effective_style_rule (and others)
depend on the definition of class CSSImportRule.
This hasn't caused any problems so far because CSSStyleSheet.h happened
to be always included after CSSImportRule.h (in part due to alphabetical
ordering).
However, a compilation unit that (for example) only contains
#include <Userland/Libraries/LibWeb/CSSImportRule.h>
would fail to compile.
This patch resolves this issue by pushing the inline definition of
Web::CSS::CSSStyleSheet::for_each_effective_style_rule and
for_first_not_loaded_import_rule into a different file, and adding the
missing headers.
This patch makes both of these classes inherit from RefCounted and
Bindings::Wrappable, plus some minimal rejigging to allow us to keep
using them internally while also exposing them to web content.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
