test(cli/dts): typecheck examples in declaration files (#10707)

This commits adds two integration tests that typecheck examples
in the docstrings in Deno declaration files.

cli/dts/lib.deno.unstable.d.ts

@@ -139,10 +139,7 @@ declare namespace Deno {
    * // The Deno.core namespace is needed to interact with plugins, but this is
    * // internal so we use ts-ignore to skip type checking these calls.
    * // @ts-ignore
-   * const {
+   * const { op_test_sync, op_test_async } = Deno.core.ops();
-   *   op_test_sync,
-   *   op_test_async,
-   * } = Deno.core.ops();
    *
    * assert(op_test_sync);
    * assert(op_test_async);

cli/tests/integration_tests.rs

@@ -18,6 +18,39 @@ use tempfile::TempDir;
 use test_util as util;
 use tokio::task::LocalSet;
 
+// TODO(caspervonb): investiate why this fails on Windows.
+#[cfg(unix)]
+#[test]
+fn typecheck_declarations_ns() {
+  let status = util::deno_cmd()
+    .arg("test")
+    .arg("--allow-all")
+    .arg("--doc")
+    .arg(util::root_path().join("cli/dts/lib.deno.ns.d.ts"))
+    .spawn()
+    .unwrap()
+    .wait()
+    .unwrap();
+  assert!(status.success());
+}
+
+// TODO(caspervonb): investiate why this fails on Windows.
+#[cfg(unix)]
+#[test]
+fn typecheck_declarations_unstable() {
+  let status = util::deno_cmd()
+    .arg("test")
+    .arg("--doc")
+    .arg("--allow-all")
+    .arg("--unstable")
+    .arg(util::root_path().join("cli/dts/lib.deno.unstable.d.ts"))
+    .spawn()
+    .unwrap()
+    .wait()
+    .unwrap();
+  assert!(status.success());
+}
+
 #[test]
 fn js_unit_tests_lint() {
   let status = util::deno_cmd()

cli/tests/integration_tests_lsp.rs

@@ -318,7 +318,7 @@ fn lsp_hover_unstable_enabled() {
           "language":"typescript",
           "value":"function Deno.openPlugin(filename: string): number"
         },
-        "**UNSTABLE**: new API, yet to be vetted.\n\nOpen and initialize a plugin.\n\n```ts\nimport { assert } from \"https://deno.land/std/testing/asserts.ts\";\nconst rid = Deno.openPlugin(\"./path/to/some/plugin.so\");\n\n// The Deno.core namespace is needed to interact with plugins, but this is\n// internal so we use ts-ignore to skip type checking these calls.\n// @ts-ignore\nconst {\n op_test_sync,\n op_test_async,\n} = Deno.core.ops();\n\nassert(op_test_sync);\nassert(op_test_async);\n\n// @ts-ignore\nconst result = Deno.core.opSync(\"op_test_sync\");\n\n// @ts-ignore\nconst result = await Deno.core.opAsync(\"op_test_sync\");\n```\n\nRequires `allow-plugin` permission.\n\nThe plugin system is not stable and will change in the future, hence the\nlack of docs. For now take a look at the example\nhttps://github.com/denoland/deno/tree/main/test_plugin"
+        "**UNSTABLE**: new API, yet to be vetted.\n\nOpen and initialize a plugin.\n\n```ts\nimport { assert } from \"https://deno.land/std/testing/asserts.ts\";\nconst rid = Deno.openPlugin(\"./path/to/some/plugin.so\");\n\n// The Deno.core namespace is needed to interact with plugins, but this is\n// internal so we use ts-ignore to skip type checking these calls.\n// @ts-ignore\nconst { op_test_sync, op_test_async } = Deno.core.ops();\n\nassert(op_test_sync);\nassert(op_test_async);\n\n// @ts-ignore\nconst result = Deno.core.opSync(\"op_test_sync\");\n\n// @ts-ignore\nconst result = await Deno.core.opAsync(\"op_test_sync\");\n```\n\nRequires `allow-plugin` permission.\n\nThe plugin system is not stable and will change in the future, hence the\nlack of docs. For now take a look at the example\nhttps://github.com/denoland/deno/tree/main/test_plugin"
       ],
       "range":{
         "start":{