no-redundant-undefined: enforce undefined for optional parameters

[sandersn]

Previously, both optional parameters and optional properties forbid undefined in their type. Now optional properties require it so that people can use exactOptionalPropertyTypes with packages from DT.

To avoid "no-redundant-undefined means redundant-undefined!?", I also renamed the lint rule. There are only 17 projects that turn off this rule, so I think it's easy to rename along with all the other changes that this rule will cause in DT.

[sandersn]

I'm going to wait to merge this until I can clean up DT to pass -- and I need to ship a new version of dtslint in a day or two for the beta before then.

[sandersn]

@wandyezj points out that it doesn't make sense to require optional properties to have undefined in their type now that there's a semantic distinction. Lots of packages will want to disallow it now that that's possible.

However, plenty of people won't know about the distinction at first, meaning that some new types will incorrectly exclude undefined. I don't think it can be helped, though, so I'm going to remove the requirement for properties now that I've used it to upgrade them.

I expect over time that @a-tarasyuk's eslint rule will grow configuration options that allow people either to upgrade old code or keep new code appropriately strict.