feat: CSS3 filter support - #1

This PR implements CSS3 filter support for NativeScript, addressing issue NativeScript#1428.

What's Included

• New ilter CSS property that accepts filter functions:
  • �lur(px)
  • �rightness(%)
  • contrast(%)
  • grayscale(%)
  • saturate(%)
  • invert(%)
  • sepia(%)
  • hue-rotate(deg/rad/grad/turn)
  • drop-shadow(offset-x offset-y blur-radius color?)
  • opacity(%) (note: opacity already exists as a separate property)

Implementation Details

• Parser: Added ilter-parser.ts to parse filter functions into structured data.
• Style Property: Registered ilterProperty in style-properties.ts.
• iOS: Uses Core Image filters (CIGaussianBlur, CIColorControls, CISepiaTone, CIHueAdjust, CIColorInvert) and layer shadow for drop-shadow.
• Android: Uses RenderEffect (API 31+) with ColorMatrix for color adjustments and BlurEffect for blur. drop-shadow not fully implemented on Android due to platform limitations.

Tests

• Added unit tests for the filter parser in ilter-parser.spec.ts.

Notes

• The opacity filter function directly sets view alpha; may conflict with the existing opacity property.
• Some filter functions may not be supported on older Android versions (pre-API 31).

Fixes NativeScript#1428