fix: proxy non-promised methods in browser-snippet

[justin-fiedler]

Summary

AMP-85112

Non-promised functions are not being properly queued in the Browser snippet. There is existing logic in browser-client.ts, but I don't think that works in the proxy case.

<script>
// load snippet function
!function(...)

amplitude.init()
<script>
<script>
   assertFalse(amplitude.invoked)
   amplitude.setUserId("user-1")

   setTimeout(() => {
      assertTrue(amplitude.invoked)
      const userId = amplitude.getUserId()
      // userId is undefined
   }, 3000)
<script>

I added new logic in the snippet to proxy non-promise methods.

[kevinpagtakhan]

There is existing logic in browser-client.ts, but I don't think that works in the proxy case.

This logic is added for the situation where the SDK is already loaded, but operations are called before init.

[kevinpagtakhan]

🚀