Fix SIMD intrinsics handling in crossgen2 (dotnet/coreclr#27853)

Fix SIMD intrinsics handling in crossgen2 (dotnet/coreclr#27853)

* Fix SIMD intrinsics handling in crossgen2

Crossgen2 was compiling methods that call SIMD intrinsics
(System.Numerics.Vector<T>). This is not correct, as the size of the
vector is a runtime specific detail - e.g. when running on devices
without SSE2 support, the size is 4 and when running on devices with
SSE2 support, the size is 8.
This fixes runtime errors in 6 coreclr pri 0 tests.

* Reflect PR feedback

Create a IsVectorOfT method and use it at all places where we were
previously checking the namespace and type name of Vector<T>

Commit migrated from https://github.com/dotnet/coreclr/commit/0f9814cc4e25ee4060d8f3ae2305210aef94f1bc