- `fail_fast`,`basic_string_span` and `basic_zstring_span` are not declared in the headers any more.
- Name the exporting header file for all types in `GSL.natvis`.
VS 2019 doesn't seem to match -1 for size_t template parameter, as a result dynamic span/basic_string_span/basic_zstring_span show extent as `extent = 4294967295` (for 32-bit builds). This change updates details::extent_type to have static constexpr size_ parameter for non-dynamic span/basic_string_span/basic_zstring_span and simplifies/removes dynamic versions from GSL.natvis
fixes#856