Skip Performance timeOrigin test on macOS hosts (#56991)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/56991

The `timeOrigin` test in `Performance-itest` compares
`performance.now() + performance.timeOrigin` against `Date.now()`. On
macOS this comparison is unreliable because `performance.now()` is
backed by a monotonic clock that does NOT advance while the system is
asleep, so the monotonic time drifts relative to wall time the longer
the machine has been running.

Use the new `Fantom.getHostPlatform()` to skip just this test on macOS
hosts while keeping it active on other platforms. A comment explains
why the test cannot be run there.

Also adds a small test verifying that `performance.timeOrigin` is a
positive number and is stable across calls.

Changelog: [Internal]

Reviewed By: javache

Differential Revision: D106669674

fbshipit-source-id: 8d619216f50897554bacfd96d311276870b48839