* [Parser] Update 'Confusables.def' file to include confusable and base character names
* [Parser] Add a new utility method to return the names of the confusable and base characters for a given confusable codepoint
* [Parser] Update diagnostic for confusable character during lexing to mention confusable and base character names
* [Sema] If there is just a single confusable character, emit a tailored diagnostic that also mentions the character names
* [Diagnostics] Add new diagnostic messages to the localization file
* [Test] Update confusables test
* [Utils] Update unicode confusables txt file and update script to regenerate confusables def file
* [Parse] Regenerate 'Confusables.def' using updated script
* [Utils] Adjust generate_confusables script based on review feedback
Fix a mistake with name mapping. Updated header comment. Fix a couple of linting issues.
* [Parse] Regenerate 'Confusables.def' file once again after script changes
* [Parse] Add the newline after end of 'getConfusableAndBaseCodepointNames' method
* [Test] Update diagnostic message in 'Syntax/Parser/diags.swift'
* [Diagnostics] Update 'does not override' diagnostic message to include protocol context as well
* [Sema] Check whether the override context is a class or a protocol for diagnostic purposes
* [Test] Update tests with new diagnostic message for overrides in protocol context
* [Sema] Adjust diagnostic for overrides in structs and enums to use the existing 'override_nonclass_decl' diagnostic
This change permits a subclass to redeclare an unavailable member from a superclass. For instance, suppose you write this code (or, more likely, a version where `Base` is an ObjC class):
```swift
class Base {
@available(*, unavailable) init() {}
}
class Derived: Base {
/* override */ init() {}
}
```
Previously, Swift would reject `Derived.init()` without the `override` keyword, telling you that you should add it, but it would also reject it *with* the `override` keyword, telling you that you can't override something that's unavailable. This PR makes Swift accept it without the `override` keyword; declaring it with the keyword is still forbidden.
Fixes rdar://65702529.
