Add RNTester-visionOS scheme

[Saadnajmi]

Please select one of the following

• I am removing an existing difference between facebook/react-native and microsoft/react-native-macos 👍
• I am cherry-picking a change from Facebook's react-native into microsoft/react-native-macos 👍
• I am making a fix / change for the macOS implementation of react-native
• I am making a change required for Microsoft usage of react-native

Summary:

This PR is part of a series of PRs for adding support for visionOS to the repository. See #2019 .

Add a new scheme for RNTester-visionOS. This won't compile as is, we're still missing the visionOS native changes/ifdefs. I want to split this PR out anyway to keep the changes per PR smaller, and to split out the pbxproj and Xcode changes from the objective C changes.

Changelog:

[INTERNAL] [ADDED] - Add RNTester-visionOS scheme

Test Plan:

CI should pass.