[mmp] Add stripping of 32-bit dylibs to work with new App Store restr…

[chamons]

…ictions (#3387)

• [macOS]Mac App failed to publish with error:"Unsupported Architectures. Your executable contained the following disallowed architectures: '[i386 Payload/MacCoolApp.app/Contents/MonoBundle/libMonoPosixHelper.dylib)]" #3367
• App Store will now fail builds if you add in a 32-bit dylib
• If you are a 32-bit app you don't need the 64-bit part of your fat
  dylib anyway
• Add --optimize=-trim-architectures to allow customization of behavior, as not everyone
  uses app store

In addition, while writing tests for this is was noticed that mmp tests did not "really" run Release configuration correctly in most cases. Fixing this turned out to be a bit of a pain, but necessary to correctly test this (and other things).

• Turns out that /p:configuration:debug is not sufficient to tell mmp to
  do the right thing
• That, in most projects, sets the DebugSymbols property, which really
  is what is checked.
• However, two of our projects did not have that, so we always did
  release mmp work.
• Removed configuration property for tests and added real "Release"
  configuration option

[monojenkins]

Build failure

[rolfbjarne]

Test failures are unrelated

• mscorlib/iOS 32-bit: TimeZoneTest.TestCtors (D02)
• xammac tests: MonoTouchFixtures.CoreMidi.MidiThruConnectionTests.FindTest: 2 midi connections