[6.2] [AST & Runtime] Correctly mangle extended existentials with inverse requirements

[Azoy]

• Explanation: Currently, the ASTMangler has 2 ways of emitting an extended existential mangling: 1. if the extended existential is parameterized, it will eagerly try to symbolically reference the extended shape or 2. just as a flat string. For extended existentials that have inverses, it was taking the 2nd option. The runtime does not currently have the capabilities to decode an extended existential without a shape referenced in the type mangling, so when attempting to create metadata for something like any ~Copyable it would fail spectacularly.
• Risk: Medium. Changes how the compiler mangles extended existentials with inverse requirements. It doesn't add or remove mangling rules, just uses a different form of mangling it already knows how to demangle at runtime.
• Testing: Tested by an interpreter test.
• Issue: rdar://150219645
• Reviewer: @slavapestov
• Main branch PR: [AST & Runtime] Correctly mangle extended existentials with inverse requirements #81365

[Azoy]

@swift-ci please test

[Azoy]

@swift-ci please test Windows