build: add VSCode extension recommendations (#28784)

Previously, the VSCode settings for the workspace specified the
`clang-format.executable` setting to configure auto-formatting to use
`clang-format`. Yet, this setting has no effect without the extension
that provides that configuration option namely [xaver.clang-format][1]).
For people that didn't have the extension installed, VSCode would use
the default formatters, resulting in vastly different file fomatting.

This commit adds a set of [rcommended workspace extensions][2], to help
people get the right extensions when checking out the repository.

The recommended extensions are:
- [gkalpak.aio-docs-utils][3]:
  Utilities to aid in authoring/viewing Angular documentation source
  code. Currently, mainly aid in working with
  `{@example}`/`<code-example>` tags.
- [ms-vscode.vscode-typescript-tslint-plugin][4]:
  Add auto-linting for TS files using `tslint` while editing.
- [xaver.clang-format][1]:
  Add auto-formatting for JS/TS files using `clang-format`.

[1]: https://marketplace.visualstudio.com/items?itemName=xaver.clang-format
[2]: http://go.microsoft.com/fwlink/?LinkId=827846
[3]: https://marketplace.visualstudio.com/items?itemName=gkalpak.aio-docs-utils
[4]: https://marketplace.visualstudio.com/items?itemName=ms-vscode.vscode-typescript-tslint-plugin

PR Close #28784

.vscode/extensions.json

@@ -0,0 +1,11 @@
+{
+  // See http://go.microsoft.com/fwlink/?LinkId=827846 to learn about workspace recommendations.
+  // Extension identifier format: ${publisher}.${name}. Example: vscode.csharp
+
+  // List of extensions which should be recommended for users of this workspace.
+  "recommendations": [
+    "gkalpak.aio-docs-utils",
+    "ms-vscode.vscode-typescript-tslint-plugin",
+    "xaver.clang-format",
+  ],
+}

.vscode/settings.json

@@ -5,7 +5,8 @@
   "[typescript]": {
     "editor.formatOnSave": true,
   },
-  // Please install http://clang.llvm.org/docs/ClangFormat.html in VSCode to take advantage of clang-format
+  // Please install https://marketplace.visualstudio.com/items?itemName=xaver.clang-format to take advantage of `clang-format` in VSCode.
+  // (See https://clang.llvm.org/docs/ClangFormat.html for more info `clang-format`.)
   "clang-format.executable": "${workspaceRoot}/node_modules/.bin/clang-format",
   "files.watcherExclude": {
     "**/.git/objects/**": true,