Per [range.view]/6, a `view_interface` isn't a base class of itself, so
`enable_view` should report `false`. Also, current implementation
strategy handles `const` but not `volatile`, IIUC cv-qualifiers should
be consistent handled.
In `enable_view.compile.pass.cpp`, coverage for (`const`) `volatile`
types are added.
Drive-by: Remove one unnessary `test_macro.h` inclusion in a test.
Fixes#132577.