Swift 6, SwiftUnicodeDataTables, Other Improvements

[STREGA]

Moves the package to Swift 6 and the Package tools version to swift 6.
Since Embedded is only available using Swift 6 toolchain, it only seems logical to require the baseline language version.

Also moves the helper variables to the bottom of Package.swift and converts them to computed variables.
When the helper variables are constants they can be filled in before the Context.environment is populated leading to compile errors. This change will help reduce build errors when users copy the variables from PlaydateKit to their own package.

[STREGA]

Added support for linking SwiftUnicodeDataTables.
In my testing the compiled pdx is the same size as when linked and not linked, when not using any functions that requires the unicode stuff. So this linking is on by default, but a new argument --disableSwiftUnicodeDataTables is added just in case there's a problem in the future. The fix is kind of a hack so the Playdate SDK changing could break the hack.

[STREGA]

Use the plugins PlaydateSDK path for pdc CLI
Show the build path in output to make finding it easier for users