fix(ios): FirebaseCrashlytics release mode and delegate handling improvements

[NathanWalker]

• fixes FirebaseCrashlytics import in release mode (see attachments) - When building in release mode for store upload the module import would cause error
• improves delegate handling to retain on the firebase symbol to avoid occasional early garbage collection by v8 engine
• fixes random crash when trying to login with Google on iOS with {N} 7

This is published under rc right now with @nativescript/firebase 11.1.1-rc.0 if anyone experiences issues related to above can try and please confirm here if it solved it for you.

[romandrahan]

It looks like #1640 (comment) has been resolved here 👍

[EddyVerbruggen]

Ah, nice, I missed this PR and fixed that first issue in the same way :)
Merging! Thank you @NathanWalker!

[lambourn]

minor: the semicolon causes a warning when main.m gets processed

warning: extra tokens at end of #import directive [-Wextra-tokens]
#import <FirebaseCrashlytics/FirebaseCrashlytics.h>;

[EddyVerbruggen]

@lambourn lol, that's probably why Github says there's a merge conflict on that line :)