Configurable Generic Constraints for Swift

[snowsignal]

Resolves #86.

Default type constraints can now be specified for Swift within the config, using default_generic_constraints = [...] under [swift]. Constraint strings within the list can include multiple constraints, such as Sendable & Identifiable.

[CerulanLumina]

Looks good so far, needs further tests as mentioned.

[kevinbhayes]

The default typeshare.toml specification worked, but if I didn't specify it there, and tried to apply it to a single type, it did nothing. For example:

#[typeshare(swift(generic_decorators = "Sendable & Codable"))]
#[derive(Serialize, Debug)]
#[serde(rename_all = "camelCase")]
pub struct MyMenuEntry<A> {

generated:

public struct MyMenuEntry<A: Codable>: Codable, Sendable

[snowsignal]

@kevinbhayes I've been trying to fix this - it looks like parenthesized parameters like swift(...) were being ignored by the Swift codegen code, and this issue runs deeper than I expected.

[kevinbhayes]

@kevinbhayes I've been trying to fix this - it looks like parenthesized parameters like swift(...) were being ignored by the Swift codegen code, and this issue runs deeper than I expected.

If you want to break that part off into a separate issue, that's ok with me. I think we'll be using the toml definitions anyway.

[snowsignal]

@kevinbhayes Okay, I'll split this PR.

[kevinbhayes]

Tested by adding Sendable to default_generic_constraints = ["Sendable"] and it produced MyStruct<A: Codable & Sendable>: Codable so all is good!