feat: Add backdrop-filter CSS attribute js support

[marcinszalski-callstack]

Summary:

This PR adds JS support for the backdrop-filter style property. It follows the CSS Filters spec as applied to backdrop rendering. The property accepts the same FilterFunction type already used by the filter property, so no new types are introduced — the existing array and string parsing via processFilter is reused directly.

Supported filter functions: blur, brightness, contrast, grayscale, sepia, saturate, invert, hue-rotate, drop-shadow.

Note: opacity() and drop-shadow() are parsed and accepted without error, but are effectively no-ops in a backdrop-filter context — opacity() reveals the unfiltered content beneath, and drop-shadow() operates on the rectangular backdrop image rather than content-shaped output, producing no visible result. This matches expected CSS spec behavior.

Work has been split into three PRs for more convenient reviewing. This part adds JS parsing, type wiring, and the example page. Native rendering is covered by the iOS and Android PRs.

Changelog:

[GENERAL] [ADDED] - Add backdrop-filter CSS style property JS support

Test Plan:

Merge the iOS and Android PRs into this branch, then run the RNTester app.

• Test the Backdrop Filter screen in RNTester (BackdropFilterExample.js)
• JS parser integration tests (processBackdropFilter-itest.js)