[dev][fix] use NPM pathing when running bundlesize

check_bundle.sh assumes it will be invoked by package.json with an NPM
PATH environment. This means you can't run it directly without the
bundlesize executable in your PATH.

The issue is resolved by wrapping the `bundlesize` invocation in npx.
Since [npx will auto-install by default], disable that behavior for
safety since the assumption is that the script will be invoked from the
MobileFrontend repo.

Unfortunately, CI does not have npx so the following hack is used
instead:

  PATH="$(npm bin):$(npm bin -g):$PATH" bundlesize

That is, get the local package.json executable directory, get the global
bin directory too, and prepend it to PATH.

[npx will auto-install by default]: npm/npx#9

Change-Id: I2e13633b1394ad7d7f2ede56416ca932a82a63db

dev-scripts/check_bundle.sh

@@ -21,7 +21,7 @@ Try running `npm run build` again or removing the node_modules folder and runnin
 eof
 			exit 1;
 	}
-	bundlesize
+	PATH="$(npm bin):$(npm bin -g):$PATH" bundlesize
 	echo 'Your changes look good!'
 	exit 0;
 }