Stop using deprecated ParserErrorCode.UNEXPECTED_TOKEN.

In https://dart-review.googlesource.com/c/sdk/+/444921, all analyzer
error constants were renamed to camelCase, but
ParserErrorCode.UNEXPECTED_TOKEN was left in place (and deprecated)
since it is used by dart_style.

This change updates dart_style to use the new camelCase declaration.

Author: stereotype441

lib/src/dart_formatter.dart

@@ -200,7 +200,7 @@ final class DartFormatter {
           source: stringSource,
           offset: token.offset - inputOffset,
           length: math.max(token.length, 1),
-          diagnosticCode: ParserErrorCode.UNEXPECTED_TOKEN,
+          diagnosticCode: ParserErrorCode.unexpectedToken,
           arguments: [token.lexeme],
         );
         throw FormatterException([error]);

pubspec.yaml

@@ -9,7 +9,7 @@ environment:
   sdk: ^3.7.0
 
 dependencies:
-  analyzer: ^8.1.0
+  analyzer: ^8.2.0
   args: ^2.0.0
   collection: ^1.19.0
   package_config: ^2.1.0