A string lookup should be provided for macros

[PathogenDavid]

Right now macros are organized in an immutable array, but it can be helpful to look them up by name without just evaluating them blindly.

We should consider providing a lazily-created ImmutableDictionary of them in addition to the array.

This came up when manually translating PortAudio's macro-style enums, which do not have identifying prefixes and had to be listed manually. (EG: PaSampleFormat)

On the flip side however, it might be kinda non-obvious why we offer both (iterating an array is valuable for certain libraries, IE: Win32.) Maybe the dictionary should only be internal?

[PathogenDavid]

Mochi.DearImGui's ImVersionConstantsTransformation would also benefit from this.