draft: experimental implementation of isHittable via snapshot-to-element resolution

[ikharebashviliGD]

Summary

This PR explores an optimized implementation of the isHittable attribute for the /source endpoint, based on reviewer suggestions.

Instead of resolving each element on demand (via queries), I pre-resolve all XCUIElement instances using fb_filterDescendantsWithSnapshots, and then match them back to each snapshot in the hierarchy using their fb_uid.

The goal is to improve performance by avoiding repeated queries during tree traversal, while still exposing accurate runtime XCUIElement.hittable values.

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Key Implementation Steps

• Flattened the snapshot tree using fb_flattenTree
• Resolved matching XCUIElement instances via fb_filterDescendantsWithSnapshots
• Mapped snapshot.uid → element
• Extracted .hittable directly from matched elements
• Added isHittable to the tree only when not excluded

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What observed

In practice, this resolution appears inaccurate in many cases:

• Elements such as Application, Window, Image, and Other consistently report isHittable: YES
• This contradicts the runtime behavior observed when using query-based resolution (descendantsMatchingType + matchingIdentifier)
• Validated this by comparing JSON source outputs side-by-side (attached in main PR)

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📎 Related to main discussion: appium#1021
📎 Issue reference: [Feat] - Add isHittable to iOS driver appium#1005