Add Java-idiomatic camelCase aliases for core geometry helpers

[Copilot]

This port intentionally retained many C#-style public APIs; this change starts smoothing that edge by exposing Java-idiomatic method names in core geometry types while preserving existing behavior. The update is intentionally narrow and backward-compatible.

• Core API ergonomics (non-breaking aliases)

  • Added camelCase aliases in Rect64:
    • asPath, isEmpty, isValid, midPoint, contains(...), intersects(...)
  • Added camelCase aliases in RectD:
    • asPath, isEmpty, midPoint, contains(...), intersects(...)
  • Added camelCase alias in PointD:
    • negate

• Compatibility model

  • Existing PascalCase methods remain unchanged and continue to be the canonical implementations.
  • New camelCase methods delegate directly to the existing methods to avoid behavioral drift.

• Documentation alignment

  • Updated README “Port Info” note to clarify:
    • Clipper static methods remain PascalCase
    • core geometry types now expose Java-style camelCase aliases.

• Focused coverage for alias parity

  • Added TestJavaIdiomaticAliases to assert that each new alias returns the same result as its PascalCase counterpart.

Rect64 rect = new Rect64(0, 0, 10, 10);

// Existing API
boolean a = rect.IsEmpty();

// Java-idiomatic alias (same behavior)
boolean b = rect.isEmpty();

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