feat: syntax highlighting for .bazelrc

The main purpose here is really to prevent vscode from autodetecting
.bazelrc as a shell file, resulting in complaints about syntax that
isn't valid in a bash script, or mistakenly highlighting e.g. variable
expansions as if they were actually honored in a .bazelrc.

We can also do a bit better, by actually understanding the semantics of
e.g. config specifiers and so on.

This does _not_ try to exhaustively match the list of all possible
flags, and so it can make mistakes like treating --copt -O3 as if it
were two separate flags rather than a flag + value, however that's
mostly harmless.  Maintaining a list of known flags would be
prohibitively difficult to maintain without some kind of automation.

There is special treatment for a couple of flags, including
`--config` and a few flags that expect regex arguments, like
`--instrumentation_filter`.

Closes bazel-contrib#259

package.json

@@ -251,13 +251,29 @@
             }
         ],
         "grammars": [
+            {
+                "language": "bazelrc",
+                "scopeName": "source.bazelrc",
+                "path": "./syntaxes/bazelrc.tmLanguage.json"
+            },
             {
                 "language": "starlark",
                 "scopeName": "source.starlark",
                 "path": "./syntaxes/starlark.tmLanguage.json"
             }
         ],
         "languages": [
+            {
+                "id": "bazelrc",
+                "extensions": [
+                    ".bazelrc"
+                ],
+                "filenames": [
+                    ".bazelrc",
+                    "bazel.rc"
+                ],
+                "configuration": "./syntaxes/bazelrc.configuration.json"
+            },
             {
                 "id": "starlark",
                 "aliases": [

syntaxes/bazelrc.configuration.json

@@ -0,0 +1,33 @@
+{
+    "comments": {
+        "lineComment": "#"
+    },
+    "autoClosingPairs": [
+        {
+            "open": "\"",
+            "close": "\"",
+            "notIn": [
+                "string",
+                "comment"
+            ]
+        },
+        {
+            "open": "'",
+            "close": "'",
+            "notIn": [
+                "string",
+                "comment"
+            ]
+        }
+    ],
+    "surroundingPairs": [
+        [
+            "\"",
+            "\""
+        ],
+        [
+            "'",
+            "'"
+        ]
+    ]
+}