Optimize TextAlignmentExtensionsGenerator

[brminnick]

Description of Change

This PR improves the performance of TextAlignmentExtensionsGenerator, optimizing for memory allocations and processing time.

This PR also adds Unit Tests + Benchmarks for CommunityToolkit.Maui.Markup.SourceGenerators to ensure no regressions between the previous implementation of TextAlignmentExtensionsGenerator and this updated/optimized implementation.

PR Checklist

• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard

Additional information

[brminnick]

Here's the current benchmark results. It looks like I still have some work to do to optimize the SourceGenerator to reduce memory allocations

Current / Previous TextAlignmentExtensionsGenerator

Method	Mean	Error	StdDev	Median	Gen0	Allocated
VerifyGeneratedSource_WhenClassIsGeneric	70.92 ms	7.361 ms	20.15 ms	61.36 ms	333.3333	9.48 MB
VerifyGeneratedSource_WhenClassImplementsITextAlignmentInterface	67.18 ms	4.793 ms	12.96 ms	61.78 ms	333.3333	9.4 MB

Updated TextAlignmentExtensionsGenerator

Method	Mean	Error	StdDev	Median	Gen0	Allocated
VerifyGeneratedSource_WhenClassIsGeneric	65.35 ms	5.100 ms	14.13 ms	59.63 ms	333.3333	10.49 MB
VerifyGeneratedSource_WhenClassImplementsITextAlignmentInterface	66.48 ms	6.051 ms	16.67 ms	58.66 ms	333.3333	10.42 MB