fix: highlight upcast as a keyword in grammar

Add `upcast` to the `as|is` keyword patterns so it is tokenized as
`keyword.operator.type.php` instead of `constant.other.php`.

Co-Authored-By: Claude <svc-devxp-claude@slack-corp.com>

Author: mszabo-wikia

syntaxes/hack.json

@@ -1376,7 +1376,7 @@
           "name": "keyword.operator.logical.php"
         },
         {
-          "begin": "(?i)\\b(as|is)\\b\\s+(?=[\\\\$a-z_])",
+          "begin": "(?i)\\b(as|is|upcast)\\b\\s+(?=[\\\\$a-z_~?])",
           "beginCaptures": {
             "1": {
               "name": "keyword.operator.type.php"
@@ -1393,7 +1393,7 @@
           ]
         },
         {
-          "match": "(?i)\\b(is|as)\\b",
+          "match": "(?i)\\b(is|as|upcast)\\b",
           "name": "keyword.operator.type.php"
         },
         {

test/grammar/upcast.hack

@@ -0,0 +1,6 @@
+type upcast_test_t = shape('x' => string);
+
+function upcast_test(dynamic $b): void {
+    $var = $b upcast ~int;
+    $upcast = 'test';
+}

test/grammar/upcast.hack.snap

@@ -0,0 +1,63 @@
+# SYNTAX TEST "source.hack" "autogenerated snapshot test"
+>type upcast_test_t = shape('x' => string);
+#^^^^ source.hack meta.typedecl.php storage.type.typedecl.php
+#    ^ source.hack meta.typedecl.php
+#     ^^^^^^^^^^^^^ source.hack meta.typedecl.php entity.name.type.typedecl.php
+#                  ^ source.hack meta.typedecl.php
+#                   ^ source.hack meta.typedecl.php keyword.operator.assignment.php
+#                    ^ source.hack meta.typedecl.php
+#                     ^^^^^^ source.hack meta.typedecl.php storage.type.shape.php
+#                           ^ source.hack meta.typedecl.php storage.type.shape.php string.quoted.single.php punctuation.definition.string.begin.php
+#                            ^ source.hack meta.typedecl.php storage.type.shape.php string.quoted.single.php meta.string-contents.quoted.single.php
+#                             ^ source.hack meta.typedecl.php storage.type.shape.php string.quoted.single.php punctuation.definition.string.end.php
+#                              ^^^^ source.hack meta.typedecl.php storage.type.shape.php
+#                                  ^^^^^^ source.hack meta.typedecl.php storage.type.shape.php support.type.php
+#                                        ^ source.hack meta.typedecl.php storage.type.shape.php keyword.operator.key.php
+#                                         ^ source.hack meta.typedecl.php punctuation.termination.expression.php
+>
+#^ source.hack
+>function upcast_test(dynamic $b): void {
+#^^^^^^^^ source.hack meta.function.php storage.type.function.php
+#        ^ source.hack meta.function.php
+#         ^^^^^^^^^^^ source.hack meta.function.php entity.name.function.php
+#                    ^ source.hack meta.function.php punctuation.definition.parameters.begin.php
+#                     ^^^^^^^ source.hack meta.function.php meta.function.arguments.php support.class.php
+#                            ^ source.hack meta.function.php meta.function.arguments.php
+#                             ^ source.hack meta.function.php meta.function.arguments.php variable.other.php punctuation.definition.variable.php
+#                              ^ source.hack meta.function.php meta.function.arguments.php variable.other.php
+#                               ^ source.hack meta.function.php punctuation.definition.parameters.end.php
+#                                ^ source.hack meta.function.php punctuation.definition.type.php
+#                                 ^ source.hack meta.function.php
+#                                  ^^^^ source.hack meta.function.php support.class.php
+#                                      ^ source.hack meta.function.php
+#                                       ^ source.hack punctuation.section.scope.begin.php
+>    $var = $b upcast ~int;
+#^^^^ source.hack
+#    ^ source.hack variable.other.php punctuation.definition.variable.php
+#     ^^^ source.hack variable.other.php
+#        ^ source.hack
+#         ^ source.hack keyword.operator.assignment.php
+#          ^ source.hack
+#           ^ source.hack variable.other.php punctuation.definition.variable.php
+#            ^ source.hack variable.other.php
+#             ^ source.hack
+#              ^^^^^^ source.hack keyword.operator.type.php
+#                    ^ source.hack
+#                     ^ source.hack keyword.operator.bitwise.php
+#                      ^^^ source.hack support.type.php
+#                         ^ source.hack punctuation.terminator.expression.php
+>    $upcast = 'test';
+#^^^^ source.hack
+#    ^ source.hack variable.other.php punctuation.definition.variable.php
+#     ^^^^^^ source.hack variable.other.php
+#           ^ source.hack
+#            ^ source.hack keyword.operator.assignment.php
+#             ^ source.hack
+#              ^ source.hack string.quoted.single.php punctuation.definition.string.begin.php
+#               ^^^^ source.hack string.quoted.single.php meta.string-contents.quoted.single.php
+#                   ^ source.hack string.quoted.single.php punctuation.definition.string.end.php
+#                    ^ source.hack punctuation.terminator.expression.php
+>}
+#^ source.hack punctuation.section.scope.end.php
+>
+#^ source.hack