feat(crashlytics, ios): add native helper log / setCustomValue methods

user request, useful for "brownfield" apps that have custom native code and want
to use crashlytics native methods from their own native code

Author: mikehardy

packages/crashlytics/ios/RNFBCrashlytics/RNFBCrashlyticsNativeHelper.h

@@ -22,4 +22,8 @@
 
 + (void)recordNativeError:(NSError *)error;
 
++ (void)log:(nonnull NSString *)msg;
+
++ (void)setCustomValue:(nullable id)value forKey:(nonnull NSString *)key;
+
 @end

packages/crashlytics/ios/RNFBCrashlytics/RNFBCrashlyticsNativeHelper.m

@@ -25,4 +25,12 @@ + (void)recordNativeError:(NSError *)error {
   [[FIRCrashlytics crashlytics] recordError:error];
 }
 
++ (void)log:(nonnull NSString *)msg {
+  [[FIRCrashlytics crashlytics] log:msg];
+}
+
++ (void)setCustomValue:(nullable id)value forKey:(nonnull NSString *)key {
+  [[FIRCrashlytics crashlytics] setCustomValue:value forKey:key];
+}
+
 @end