Do not use default GlyphVector

[JimBobSquarePants]

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Description

Fixes #480

This pull request focuses on modernizing and simplifying the codebase by adopting collection expressions and more explicit empty initializations, as well as improving code clarity and safety. The changes primarily affect glyph loading and manipulation in the font rendering pipeline.

Key improvements include:

Modern C# Syntax and Code Simplification

• Replaced new() and Array.Empty<T>() with collection expressions ([] and [.. collection]) for initializing lists and arrays in CompositeGlyphLoader and GlyphVector, making the code more concise and up-to-date with recent C# features. [1] [2] [3] [4]

• Used index-from-end (^) operators for array assignments in GlyphVector.Hint, improving code readability when accessing elements from the end of an array.

Robustness and Explicit Return Values

• Changed the default return value in GlyphTable.GetGlyph to explicitly return GlyphVector.Empty() instead of default, clarifying intent and reducing ambiguity for empty glyphs.