Type `str` is missing `casefold` method

Prerequisites

• Are you running the latest version?
• Are you reporting to the correct repository?
• Did you perform a cursory search?

Description

Type str implementation is missing casefold method. This method was added in Python 3.3

Steps to Reproduce

1. Run ipy.exe
2. Type str.casefold and hit enter
3. See exception

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'type' object has no attribute 'casefold'

Expected behavior: [What you expected to happen]

Runtime should find the method and repor <method 'casefold' of 'str' objects>

Actual behavior: [What actually happened]

Runtime reports AttributeError

Versions

You can get this information from executing ipy -VV.

IronPython 3.4.0 (3.4.0.1000)
[.NETFramework,Version=v4.6.2 on .NET Framework 4.8.4515.0 (64-bit)]

and

IronPython 3.4.0 (3.4.0.1000)
[.NETCoreApp,Version=v6.0 on .NET 6.0.5 (64-bit)]

Reproduce the failure with ipy.exe using str.casefold on the listed IronPython versions, then locate the str type implementation. Add the missing method so the runtime reports the expected bound-method description, and verify that the AttributeError no longer occurs.