Improve the Smithy metadata matcher.

Previously, metadata foo bar baz = 23 was accepted, but according to
the definition https://smithy.io/2.0/spec/idl.html#grammar-token-smithy-MetadataSection
it should be "metadata"<whitespace>Identifier/String<optional whitespace>.

pygments/lexers/smithy.py

@@ -56,8 +56,9 @@ class SmithyLexer(RegexLexer):
             (words(aggregate_shapes,
                    prefix=r'^', suffix=r'(\s+' + identifier + r')'),
                 bygroups(Keyword.Declaration, Name.Class)),
-            (r'^(metadata)(\s+.+)(\s*)(=)',
-                bygroups(Keyword.Declaration, Name.Class, Whitespace, Name.Decorator)),
+            (r'^(metadata)(\s+)((?:\S+)|(?:\"[^"]+\"))(\s*)(=)',
+                bygroups(Keyword.Declaration, Whitespace, Name.Class,
+                         Whitespace, Name.Decorator)),
             (r"(true|false|null)", Keyword.Constant),
             (r"(-?(?:0|[1-9]\d*)(?:\.\d+)?(?:[eE][+-]?\d+)?)", Number),
             (identifier + ":", Name.Label),

tests/examplefiles/smithy/test.smithy

@@ -2,6 +2,18 @@ $version: "1.0"
 
 namespace test
 
+metadata "foo" = ["bar", "baz"]
+metadata validators = [
+    {
+        name: "ValidatorName"
+        id: "ValidatorId"
+        message: "Some string"
+        configuration: {
+            selector: "operation"
+        }
+    }
+]
+
 /// Define how an HTTP request is serialized given a specific protocol,
 /// authentication scheme, and set of input parameters.
 @trait(selector: "operation")