[minor]: enumeration macros

[tayloraswift]

why a lowercase name for @ambient?

because @ambient is languagey. @Discriminated and @Projection are not languagey, i just made them up myself.

[gemini-code-assist]

Code Review

This pull request introduces three new Swift macros: @ambient, @Discriminated, and @Projection, along with their implementations and comprehensive unit tests. The reviewer provided valuable feedback to make these macros more robust. Key recommendations include: safely handling enum modifiers (such as filtering out indirect and conditionally applying @inlinable based on access control), supporting non-optional associated values in @Projection by checking if the parameter type is syntactically optional, and improving optional flattening in @Projection to correctly detect unsugared optionals like Optional<T>.