Cache Functions instances by app

[morganchen12]

Fixes #7783.

[google-oss-bot]

Coverage Report

Affected SDKs

• FirebaseFunctions-iOS-FirebaseFunctions.framework

  SDK overall coverage changed from 52.17% (8dd5fdd) to 60.63% (36bcbf3) by +8.46%.

  Filename	Base (8dd5fdd)	Head (36bcbf3)	Diff
  FIRFunctions.m	54.10%	70.03%	+15.93%
  FIRFunctionsComponent.m	?	86.30%	?

Test Logs

• Base (8dd5fdd1): https://github.com/firebase/firebase-ios-sdk/actions/runs/940857298
• Head (36bcbf32): https://github.com/firebase/firebase-ios-sdk/actions/runs/941604486

[paulb777]

Is the incremental coverage checker correct with its four reports? cc: @granluo

[granluo]

Is the incremental coverage checker correct with its four reports? cc: @granluo

For the latest reports, I double checked with the xcresult artifact in this run. The reports should be correct.

[morganchen12]

Talked to Ryan offline and we agreed it'd be best to move Functions to broader FIRComponent adoption, with these specific points:

• Functions should attempt to minimize creation of new instances as much as possible
• Functions should return a new instance per combination of app, region, and custom domain

It's a bit late for code freeze, but we can punt to M99 if necessary.

[paulb777]

LGTM on green