vscode-go: add strict typecheck step to CI

Test files are excluded from strict typechecking. We plan
to fix errors in those files as needed or remove the tests
with the legacy tooling.

For golang/vscode-go#57.

Change-Id: I84ea8bc1834e2e1ee58c297fed984bb94ec0de52
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/403775
TryBot-Result: kokoro <noreply+kokoro@google.com>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
Auto-Submit: Jamal Carvalho <jamal@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

build/all.bash

@@ -45,6 +45,7 @@ run_test() {
   echo "**** Run test ****"
   df -h | grep shm
   npm ci
+  npm run typecheck
   npm run compile
   npm run unit-test
   npm test --silent

package.json

@@ -39,6 +39,7 @@
     "bundle-dev": "npm run bundle -- --sourcemap",
     "bundle-watch": "npm run bundle -- --sourcemap --watch",
     "test-compile": "tsc -p ./tsconfig.build.json",
+    "typecheck": "tsc -p ./tsconfig.strict.json --noEmit",
     "compile": "npm run bundle",
     "watch": "tsc -watch -p ./tsconfig.build.json",
     "test": "npm run test-compile && node ./out/test/runTest.js",

tsconfig.strict.json

@@ -0,0 +1,8 @@
+{
+	"extends": "./tsconfig.json",
+	"exclude": [
+		"node_modules",
+		"third_party",
+		"test"
+	]
+}