fix(analytics): use FirebaseAnalyticsCore SPM product when WithoutAdIdSupport is true

When $RNFirebaseAnalyticsWithoutAdIdSupport = true with SPM enabled,
FirebaseAnalytics pulls in GoogleAppMeasurement which contains APMETaskManager
and APMMeasurement cross-references. These cause linker errors when
FirebasePerformance is not installed.

Switch to FirebaseAnalyticsCore (-> GoogleAppMeasurementCore) in that case,
which has no IDFA and no APM symbols. CocoaPods path is unchanged.

docs: add Section 8 with 5 real integration bugs found during tvOS Xcode 26
migration and their solutions

Author: jsnavarroc