Fix IL Linking speed in CI

[adrianhall]

When building the samples/ area, all the iOS builds take 15+ minutes because of IL trimming.

See https://blog.verslu.is/maui/exclude-assemblies-from-trimming/ for details.

Using this blog as a basis, determine the best path forward to speed up the CI check.

• (PREFERRED) Potentially build with "debug" mode for the check
• set PublishTrimming option to false in csproj
• Add a Linker.xml which excludes all the relevant packages

[adrianhall]

Fixed in #531 by switching to Debug configuration.