This should be able to unblock using grpc on vision os, will add tests later
Closes#36476
COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36476 from HannahShiSFB:support-visionos edbde32d23
PiperOrigin-RevId: 630173448
Upgrade apple platform deployment_target versions to fix the cocoapods
push of BoringSSL-GRPC about the following error:
```
ld: file not found: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/arc/libarclite_macosx.a
clang: error: linker command failed with exit code 1 (use -v to see invocation)
```
ref: https://developer.apple.com/forums/thread/725300
This also aligns with the versions required by
[protobuf](https://github.com/protocolbuffers/protobuf/pull/10652)
```
ios.deployment_target = '10.0'
osx.deployment_target = '10.12'
tvos.deployment_target = '12.0'
watchos.deployment_target = '6.0'
```
Hannah Shi