Toolchain selection for Swift

[BrendanThompson]

Body

What are you proposing?

Currently the toolchain: * items only support languages that are delivered as part of Zed core. Not by extensions. It would be good to add support for languages that are provided by extensions to this. Specifically in this instance, Swift.

Why does this matter?

Swift offers a number of toolchains. Xcode, Xcode-beta, Swift OSS (swiftly). Currently there is no easy way within Zed to switch between these toolchains.

What problem does this solve?
This change would enable Swift developers to easily switch between the different toolchains in Zed.

What becomes easier or possible?
Switching toolchains for Swift becomes possible. It removes having to create profiles with different sourcekit-lsp paths.

Are there any examples or context?

The python toolchain implementation.

Possible approach

I assume that this would be possible through a similar mechanism to python

[luxmentis]

Currently the toolchain: * items only support languages that are delivered as part of Zed core. Not by extensions.

@BrendanThompson So if I understand this right, the first problem is that the extension api doesn't allow a language extension to offer a choice of toolchains? Might this be better titled as "Toolchain selection for non-core languages", rather than being Swift-specific?