Add CI checks for tvOS and visionOS

[antonis]

We should add CI checks to verify that the SDK builds and links on tvOS and visionOS.

Scope

• tvOS — RN supports it via react-native-tvos; already declared in RNSentry.podspec (s.tvos.deployment_target).
• visionOS — RN supports it via @callstack/react-native-visionos; already declared in RNSentry.podspec (s.visionos.deployment_target).

watchOS is out of scope

There is no React Native platform fork for watchOS, and the watchOS runtime has no JS engine for RN to run on. The podspec correctly omits watchos.deployment_target. A watchOS app is a pure-native target — users who want Sentry there add sentry-cocoa directly to their WatchKit target (bridged to the RN iPhone app via WatchConnectivity), which is already covered by sentry-cocoa's own CI. Nothing in @sentry/react-native runs on watchOS, so there is nothing for us to build-check.

Approach

A build-only gate (xcodebuild build with CODE_SIGNING_ALLOWED=NO) that compiles/links RNSentry against each platform, rather than a ported XCTest suite. RNSentry depends on React headers, so a standalone pod lib lint won't prove it — we need a sample app to build against.

Prerequisites

• tvOS sample — tracked in Add tvOS sample to the project #5275.
• visionOS sample — tracked in Add visionOS sample to the project #6669.

Tasks

• Add tvOS sample (Add tvOS sample to the project #5275)
• Add visionOS sample (Add visionOS sample to the project #6669)
• Add build-only CI job for tvOS (generic tvOS Simulator destination)
• Add build-only CI job for visionOS (generic xrOS Simulator destination)

[linear-code]

RN-751