Fix #76323.
* convert.cs (ImplicitConversionStandard): Move conversion of
void* to arbitrary pointer types ...
(ExplicitConversionStandard): .. here.
* ecore.cs (Expression.Error_ValueCannotBeConverted): Fix CS0266
error to always print typenames.
In tests:
* test-460.cs: New test.
In errors:
* cs0266-8.cs: New test from #76323.
svn path=/trunk/mcs/; revision=51403
