script: Implement deprecated CSSStyleSheet members (#36313)

Implements `rules`, `addRule()` and `removeRule()` for `CSSStyleSheet`.
https://drafts.csswg.org/cssom/#legacy-css-style-sheet-members

This is part of #36162

Testing:
- `/css/css-cascade/at-scope-parsing.html`
- `/css/css-conditional/at-supports-whitespace.html`
- `/css/css-nesting/invalidation-004.html`
- `/css/css-nesting/parsing.html`
- `/css/css-nesting/serialize-group-rules-with-decls.html`
- `/css/css-syntax/custom-property-rule-ambiguity.html`
- `/css/css-syntax/invalid-nested-rules.html`
- `/css/css-syntax/trailing-braces.html`
- `/css/css-syntax/var-with-blocks.html`
- `/css/css-transitions/parsing/starting-style-parsing.html`
- `/css/cssom/CSSStyleSheet.html`
- `/css/cssom/idlharness.html`
- `/css/cssom/insertRule-across-context.html`

Signed-off-by: Oriol Brufau <obrufau@igalia.com>

tests/wpt/meta/css/css-nesting/invalidation-004.html.ini

@@ -1,3 +0,0 @@
-[invalidation-004.html]
-  [CSS Selectors nested invalidation through @media by selectorText]
-    expected: FAIL

tests/wpt/meta/css/css-nesting/parsing.html.ini

@@ -1,2 +0,0 @@
-[parsing.html]
-  expected: ERROR

tests/wpt/meta/css/css-nesting/serialize-group-rules-with-decls.html.ini

@@ -1,45 +0,0 @@
-[serialize-group-rules-with-decls.html]
-  [Declarations are serialized on one line, rules on two.]
-    expected: FAIL
-
-  [Mixed declarations/rules are on two lines.]
-    expected: FAIL
-
-  [Implicit rule is serialized]
-    expected: FAIL
-
-  [Implicit rule not removed]
-    expected: FAIL
-
-  [Implicit + empty hover rule]
-    expected: FAIL
-
-  [Implicit like rule not in first position]
-    expected: FAIL
-
-  [Two implicit-like rules]
-    expected: FAIL
-
-  [Implicit like rule after decls]
-    expected: FAIL
-
-  [Implicit like rule after decls, missing closing braces]
-    expected: FAIL
-
-  [Implicit like rule with other selectors]
-    expected: FAIL
-
-  [Implicit-like rule in style rule]
-    expected: FAIL
-
-  [Empty conditional rule]
-    expected: FAIL
-
-  [Empty style rule]
-    expected: FAIL
-
-  [Empty conditional inside style rule]
-    expected: FAIL
-
-  [Empty style inside conditional]
-    expected: FAIL