Support Swift 6 language mode and Swift Syntax 600.0.0

[liamnichols]

• Closes Generated @available has trailing whitespace #97

Whitespace between @available and the opening ( causes a compile failure in Swift 6. It was found in the generated code due to how Swift Syntax 5XX.X.X would format the output.

This Pull Request does the following:

• Patches the generated code with a simple regex find and replace
• Updates the Package.swift to support Swift Syntax 600.0.0 once it is released
• Adds CI checks to run against each major Swift Syntax version
• Removes the regex workaround when using Swift Syntax 600.0.0 since the formatter in this version fixes the original whitespace issue
• Fix some deprecation warnings and removes other workarounds when using Swift Syntax 600.0.0

[github-actions]

✅ Pull Request passed benchmark checks

Summary

Wed Jun 19 10:57:59 UTC 2024

===========================================================================================================
Threshold deviations for StringGenerator.generateSource(for:tableName:accessLevel:):XCStringsToolBenchmarks
===========================================================================================================

Time (total CPU) (ms, %)	main	pull_request	Difference %	Threshold %
p25	750	965	28	5
p50	750	965	28	5
p75	793	967	22	5

New baseline 'pull_request' is WORSE than the 'main' baseline thresholds.

---

Comparing results between 'main' and 'pull_request'

Host 'Mac-1718792565479.local' with 3 'arm64' processors with 7 GB memory, running:
Darwin Kernel Version 23.5.0: Wed May  1 20:12:39 PDT 2024; root:xnu-10063.121.3~5/RELEASE_ARM64_VMAPPLE

XCStringsToolBenchmarks

StringGenerator.generateSource(for:tableName:accessLevel:) metrics

Time (total CPU) (ms) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	750	750	750	793	793	793	793	2
pull_request	965	965	965	967	967	967	967	2
Δ	215	215	215	174	174	174	174	0
Improvement %	-29	-29	-29	-22	-22	-22	-22	0

[liamnichols]

Oh, need to account for #available too