Improve error handling in "cython.array" creation code to avoid calling Py_BuildValue() with an exception set if "__pyx_format_from_typeinfo()" failed.

Avoid unnecessary int-object creation when formatting numbers as strings in format_from_typeinfo() utility function.

Improve error handling in "cython.array" creation code to avoid calling Py_BuildValue() with an exception set if "__pyx_format_from_typeinfo()" failed.

Refactor step handling in slice_memviewslice() utility code to make it more obvious what is happening in which case.
Closes GH-3568.

Avoid useless resorting to char* in nogil code in MemoryView.pyx for raising exceptions, since constant Python strings are just fine there.

See https://github.com/cython/cython/pull/3562

Rewrite _unellipsify() helper function in memoryview code to speed it up and reduce the generated C code.

See https://github.com/cython/cython/pull/3562

See #1407.

These are mutable and therefore affect the stdlib build_ext options.

Fixes #2209