Make bundle a computed property

[liamnichols]

Prior to this change, the bundle property was a custom BundleDescription enum that was a stored property, despite being the same for every value.

This causes a problem with supporting #108, because AnyClass is not Hashable so I want to work around this.

Instead, I've made bundle a computed property that returns the Foundation.Bundle directly. This is fine because the type itself ensures that it'll always be referencing the correct bundle.

This also allows me to remove the .from(_:) conversion methods.

[github-actions]

✅ Pull Request passed benchmark checks

Summary

Fri Jul 19 16:12:34 UTC 2024

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Threshold deviations for StringGenerator.generateSource(for:tableName:accessLevel:):XCStringsToolBenchmarks
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Time (total CPU) (ms, %)	main	pull_request	Difference %	Threshold %
p25	410	340	-17	5
p50	427	346	-19	5
p75	465	355	-23	5

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

---

Comparing results between 'main' and 'pull_request'

Host 'Mac-1721404154025.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): results within specified thresholds, fold down for details.

Time (total CPU) (ms) *	p0	p25	p50	p75	p90	p99	p100	Samples
main	410	410	427	465	465	465	465	3
pull_request	340	340	346	355	355	355	355	3
Δ	-70	-70	-81	-110	-110	-110	-110	0
Improvement %	17	17	19	24	24	24	24	0