Refactor generation logic so partials come after (#304)

Currently, the generator adds members to interfacelikes as we
process various IDL files. This may lead to partial interfaces
being added before the interface definition. Instead, this CL
adds partials after the interface definition, and then applies
mixins. It also dedups some logic around browser compatibility
so that we only check compatibility and process in one location.

While there is a diff in the generated files, it is functionally
the same because all we do is move members around in the same
extension type.

Author: srujzs

web/lib/src/dom/cssom.dart

@@ -352,18 +352,6 @@ extension type CSSRuleList._(JSObject _) implements JSObject {
 /// API documentation sourced from
 /// [MDN Web Docs](https://developer.mozilla.org/en-US/docs/Web/API/CSSRule).
 extension type CSSRule._(JSObject _) implements JSObject {
-  static const int KEYFRAMES_RULE = 7;
-
-  static const int KEYFRAME_RULE = 8;
-
-  static const int SUPPORTS_RULE = 12;
-
-  static const int COUNTER_STYLE_RULE = 11;
-
-  static const int FONT_FEATURE_VALUES_RULE = 14;
-
-  static const int VIEW_TRANSITION_RULE = 15;
-
   static const int STYLE_RULE = 1;
 
   static const int CHARSET_RULE = 2;
@@ -380,6 +368,18 @@ extension type CSSRule._(JSObject _) implements JSObject {
 
   static const int NAMESPACE_RULE = 10;
 
+  static const int KEYFRAMES_RULE = 7;
+
+  static const int KEYFRAME_RULE = 8;
+
+  static const int SUPPORTS_RULE = 12;
+
+  static const int COUNTER_STYLE_RULE = 11;
+
+  static const int FONT_FEATURE_VALUES_RULE = 14;
+
+  static const int VIEW_TRANSITION_RULE = 15;
+
   /// The **`cssText`** property of the [CSSRule]
   /// interface returns the actual text of a [CSSStyleSheet] style-rule.
   ///
@@ -439,11 +439,6 @@ extension type CSSRule._(JSObject _) implements JSObject {
 /// API documentation sourced from
 /// [MDN Web Docs](https://developer.mozilla.org/en-US/docs/Web/API/CSSStyleRule).
 extension type CSSStyleRule._(JSObject _) implements CSSGroupingRule, JSObject {
-  /// The **`styleMap`** read-only property of the
-  /// [CSSStyleRule] interface returns a [StylePropertyMap] object
-  /// which provides access to the rule's property-value pairs.
-  external StylePropertyMap get styleMap;
-
   /// The **`selectorText`** property of the [CSSStyleRule] interface gets and
   /// sets the selectors associated with the `CSSStyleRule`.
   external String get selectorText;
@@ -454,6 +449,11 @@ extension type CSSStyleRule._(JSObject _) implements CSSGroupingRule, JSObject {
   /// [declaration block](https://www.w3.org/TR/1998/REC-CSS2-19980512/syndata.html#block)
   /// of the [CSSStyleRule].
   external JSObject get style;
+
+  /// The **`styleMap`** read-only property of the
+  /// [CSSStyleRule] interface returns a [StylePropertyMap] object
+  /// which provides access to the rule's property-value pairs.
+  external StylePropertyMap get styleMap;
 }
 
 /// The **`CSSImportRule`** interface represents an
@@ -1930,6 +1930,7 @@ external $CSS get CSS;
 /// [MDN Web Docs](https://developer.mozilla.org/en-US/docs/Web/API/CSS).
 @JS('CSS')
 extension type $CSS._(JSObject _) implements JSObject {
+  external String escape(String ident);
   external bool supports(
     String conditionTextOrProperty, [
     String value,
@@ -1999,6 +2000,5 @@ extension type $CSS._(JSObject _) implements JSObject {
   external CSSUnitValue dpcm(num value);
   external CSSUnitValue dppx(num value);
   external CSSUnitValue fr(num value);
-  external String escape(String ident);
   external HighlightRegistry get highlights;
 }