[Android] CoreCLR uses APIs available only since Android API28

[grendello]

CoreCLR currently defines the minimum Android API level to be 21, since this is also the base level used by .NET for Android. While trying to build CoreCLR to target Android proper (and not linux-bionic), I ran into the issue of CoreCLR PAL sources using glob(3) which is available on Android only starting with API28.

The simple fix is to bump the minimum API requirement to 28, however this may limit the reach of CoreCLR on Android devices. If we don't want to do that, the glob(3) functionality would have to be implemented in-tree (or imported from another libc, for instance from musl or picolibc).

[jkotas]

This is used for emulation of FindFirstFile/FindNextFile Windows API. We should look into deleting this emulator.

[dotnet-policy-service]

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[janvorli]

It looks like the only use of the FindFirstFile / FindNextFile is in superpmi, so it should be easy to get rid of.

[janvorli]

I have removed the glob usage in #110797