Have S.L.Expressions accept conversions it incorrectly rejects. (dotnet/corefx#25768)

Have S.L.Expressions accept conversions it incorrectly rejects. (dotnet/corefx#25768)

* Have S.L.Expressions accept conversions it incorrectly rejects.

Extend the conversion checks to allow array-related explicit reference
that were rejected by Expression.Convert and Expression.CheckedConvert.

Fixes dotnet/corefx#25760, and hence fixes dotnet/corefx#25754

* Move test case that fails on netfx into separate non-netfx test

* CheckedConvert equivalent of tests

* Future-proof s_arrayAssignableInterfaces

Derive values for s_arrayAssignableInterfaces dynamically. Extra cost
is only spent once, but it will automatically deal with any future
additions to the generic interfaces supported by arrays.

Commit migrated from https://github.com/dotnet/corefx/commit/aa808b734f14a3803843bc6164678f7569f94f90