[FR]: A public api for getting the last session crash info.

### Description

We recently migrated to firebase for crash reporting purposes from AppCenter SDK. AppCenter provided us with an api to fetch the last session crash info like exception, stack trace etc. We used this in our splunk logs for debugging purposes. Are there any such apis available in firebase as well? We have considered implementing signal/exception/mach handling but that could possibly interfere with firebase's internal mechanism to detect crashes and it is also complex to implement. Can we expose an api that gives us this information?

### API Proposal

struct CrashReportSummary {
let signal: String? // e.g. SIGTRAP, SIGABRT
let exceptionName: String? // e.g. NSInvalidArgumentException
let reason: String? // Optional reason
let crashedThread: Int? // Optional thread index
}

Crashlytics.crashlytics().lastCrashReport

### Firebase Product(s)

Crashlytics