Generate SDKSettings.json file for Swift SDKs for Swift 5.9-6.0

[xtremekforever]

I know that the warnings about the SDKSettings.json file were fixed in Swift 6.1 and later and that issue #110 was closed. However, we are still generating Swift SDKs for 5.9, 5.10, and 6.0 which all give the warnings.

So, my suggestion is to generate this SDKSettings.json file for versions older than 6.1, similar to how the the Linux Static Swift SDKs do it. Here is the file that comes in the swift-6.0.3-RELEASE_static-linux-0.0.1 Swift SDK for example:

{
  "DisplayName": "Swift SDK for Statically Linked Linux (x86_64)",
  "Version": "0.0.1",
  "VersionMap": {},
  "CanonicalName": "x86_64-swift-linux-musl"
}

Taking inspiration from this, I am generating a similar file for Swift SDKs created by the generator:

{
  "CanonicalName" : "x86_64-swift-linux-gnu",
  "DisplayName" : "Swift SDK for Ubuntu Jammy (x86_64)",
  "Version" : "0.0.1",
  "VersionMap" : {

  }
}

The ordering is not the same due to how JSONEncoder() sorts things, and the formatting is a little different too due to .prettyPrinted, but it works just the same. And, the "warning: Could not read SDKSettings.json for SDK at: " warning is successfully suppressed.

This really is a minor change that is more "quality-of-life" then adding any functionality. But, not having those warnings printed when using the generated Swift SDKs are used is a nice to have.

@MaxDesiatov @euanh @kateinoigakukun

[MaxDesiatov]

Thanks! Mind adding a test for this?

[MaxDesiatov]

Overall makes sense, just a function naming nit to pick.

[MaxDesiatov]

@swift-ci test