Update the cookie and cookie-date parsers.

Avoid doing unnecessary allocations,
don't use `String.operator[]` to access single characters,
or creating substrings that are not needed.

Reuse the date-parser for cookie dates, instead of having two
separate parsers. The cookie-date-parser was very forgiving,
and only tested very little.
It's unlikely that there will be wildly different cookie formats
in actual use, when the specification only allows for one format.

Change-Id: I81b3620cc4476af3584b859f9c1eb80362f83979
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/448383
Reviewed-by: Martin Kustermann <[email protected]>
Commit-Queue: Lasse Nielsen <[email protected]>

Author: lrhn

sdk/lib/_http/http.dart

@@ -622,9 +622,7 @@ abstract interface class HeaderValue {
   factory HeaderValue([
     String value = "",
     Map<String, String?> parameters = const {},
-  ]) {
-    return _HeaderValue(value, parameters);
-  }
+  ]) => _HeaderValue(value, parameters);
 
   /// Creates a new header value object from parsing a header value
   /// string with both value and optional parameters.
@@ -636,8 +634,8 @@ abstract interface class HeaderValue {
   }) {
     return _HeaderValue.parse(
       value,
-      parameterSeparator: parameterSeparator,
-      valueSeparator: valueSeparator,
+      parameterSeparator: parameterSeparator.codeUnitAt(0),
+      valueSeparator: valueSeparator?.codeUnitAt(0) ?? _CharCode.NONE,
       preserveBackslash: preserveBackslash,
     );
   }
@@ -829,7 +827,7 @@ abstract interface class Cookie {
   /// U+0021 (`!`) through U+007E (`~`), except the separator characters:
   /// `(`, `)`, `<`, `>`, `@`, `,`, `;`, `:`, `\`, `"`, `/`, `[`, `]`, `?`, `=`,
   /// `{`, and `}`.
-  late String name;
+  abstract String name;
 
   /// The value of the cookie.
   ///
@@ -840,34 +838,34 @@ abstract interface class Cookie {
   /// `"`, `,`, `;` and `\`.
   /// Cookie values may be wrapped in a single pair of double quotes
   /// (U+0022, `"`).
-  late String value;
+  abstract String value;
 
   /// The time at which the cookie expires.
-  DateTime? expires;
+  abstract DateTime? expires;
 
   /// The number of seconds until the cookie expires. A zero or negative value
   /// means the cookie has expired.
-  int? maxAge;
+  abstract int? maxAge;
 
   /// The domain that the cookie applies to.
-  String? domain;
+  abstract String? domain;
 
   /// The path within the [domain] that the cookie applies to.
-  String? path;
+  abstract String? path;
 
   /// Whether to only send this cookie on secure connections.
-  bool secure = false;
+  abstract bool secure;
 
   /// Whether the cookie is only sent in the HTTP request and is not made
   /// available to client side scripts.
-  bool httpOnly = false;
+  abstract bool httpOnly;
 
   /// Whether the cookie is available from other sites.
   ///
   /// This value is `null` if the SameSite attribute is not present.
   ///
   /// See [SameSite] for more information.
-  SameSite? sameSite;
+  abstract SameSite? sameSite;
 
   /// Creates a new cookie setting the name and value.
   ///