bpo-45837: Properly deprecate turtle.RawTurtle.settiltangle

[hugovk]

turtle's settiltangle was deprecated in Python 3.1, according to docs:

Deprecated since version 3.1.

And the reason:

Turtle.tiltangle() has been enhanced in functionality: it now can be used to get or set the tiltangle. Turtle.settiltangle() has been deprecated.

However, in docstrings, tiltangle was accidentally commented as deprecated:

Deprecated since Python 3.1

Neither tiltangle nor settiltangle raise DeprecationWarnings.

So let's:

• Correct tiltangle's docstring to say it's not really deprecated
• Update settiltangle's docstring to say it's deprecated
• Add a DeprecationWarning to settiltangle
• Internally call self.tiltangle instead of self.settiltangle

BPO references:

• 2009 https://bugs.python.org/issue5923 - when settiltangle was originally deprecated, with rationale.

• 2010 https://bugs.python.org/issue7888 - the deprecation mixup was discovered and apparently corrected in py3k and release31-maint. I've not done the SCM archaeology to discover why this didn't make it through!

• 2020 https://bugs.python.org/issue41165 - both mentioned as deprecated, discrepancy not noted.

https://bugs.python.org/issue45837

[ambv]

@hugovk would be great if you created a 3.10 and 3.9 PR that only clarifies in its docstring that tiltangle is not in fact deprecated.

[hugovk]

Sure, please see #29629 and #29630. Do they need news entries?

[ambv]

No, they don't. Thanks, Hugo! All merged.