IPHONEOS_DEPLOYMENT_TARGET is ignored in Nx workspace

Environment Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: 8.1.2
• Cross-platform modules: 8.1.3
• Android Runtime: N/A
• iOS Runtime: 8.1.0
• XCode Version: 12.4
• Plugin(s): N/A

Describe the bug As discussed in #8772, and the suggested solution of using build.xcconfig, I'm still facing the issue while using plugin-seed repo to develop a plugin that requires the minimum target iOS version to be 11.

To Reproduce

1. Clone plugin-seed template repo.
2. Create directory apps/demo-angular/App_Resources/iOS.
3. Create file build.xcconfig in previous directory.
4. Add IPHONEOS_DEPLOYMENT_TARGET = 11.0
5. Build workspace.
6. Open xcode.
7. Find minimum target version is still at 9.0

Expected behavior Find minimum target version to change to 11.0