Fix issue where no RPC is issued when deadline is specified.

[sampajano]

The issue

This is a temporary hack to fix #1153, which is caused by goog.global not properly pointing to the proper global scope (e.g. window) when grpc-web is being imported as a CommonJS module (because this points to the module scope instead of actual global scope (i.e. globalThis)).

goog.Timer.defaultTimerObject is set to point to goog.global, and that's why it throws when setTimeout is called on it.

The fix

• In this fix, we'll try to use globalThis when possible, and if it's not available (pre-2020 browsers, etc.), fallback to self, which should work in both browsers and workers.
• Also added an interop test to verify the fix works (the new test fails without the fix)

[stanley-cheung]

LGTM