Correct SimpleBackgroundTransfer sample to export optional protocol s…

…electors (xamarin#410)

- Fixes xamarin#406
- Optional protocol methods must export if you use IFoo instead of Foo base class

[SoupChef] Fix build with Xcode 12.2 (xamarin#409)

Xcode 12.2
- adds `arm64` to the simulator architectures
- removes `i386` from the simulator architectures

`lipo` cannot create a _classic_ fat archive with `arm64` simulator and
`arm64` device slices - since they are the same architecture.

This requires `.xcframework` support which is not yet supported by XI
and XM.

However we can tweak the build to do:
- x86_64 only for simulator, which is the only support arch for XI today
- arm64 for devices

and that makes `lipo` happy and we can continue to have this sample under
test automation.

Note: the original `.a` names were incorrect as they did not match the
architectures that were present in the files. I changed them to mention
the platform.

[UICatalog] Fix ambiguous call in sample (xamarin#408)

a new API with a similar signature (wrt null) was added in XI 14

Remove invalid project from FileSystemSampleCode (xamarin#404)

The FileSystem2.csproj project does not exist, its entry has been
removed from WorkingWithTheFileSystem.sln.

Fix ColorFeed sample by adding required Info.plist keys (xamarin#393)

- xamarin#392

fix spelling mistake

[background] update project

[MemoryDemo] Make sure the same output path isn't used with multiple …

…configurations. (xamarin#395)

Make sure the same output path isn't used with multiple configurations by
using the correct configuration name in the output path.

Update README.md

Update README.md