fix: send mobile scroll distance only for direction strategy

[krayc425]

Summary

Align mobile: scroll distance handling with WDA strategy behavior and document the parameter.

WDA Behavior Reference

handleScroll in WDA evaluates strategies in this order: name -> direction -> predicateString -> toVisible.
distance is only read inside the direction branch (defaulting to 1.0).

• WebDriverAgentLib/Commands/FBElementCommands.m

NSString *const direction = request.arguments[@"direction"];
  if (direction) {
    NSString *const distanceString = request.arguments[@"distance"] ?: @"1.0";
    ...

What Changed

• Updated mobileScroll to only include distance in the payload when the direction strategy is selected.
• Added distance to mobile: scroll execute-method docs with strategy caveat.
• Added unit tests to verify:
  • distance is sent when direction is used.
  • distance is ignored when a non-direction strategy (e.g. name) is used.

[github-actions]

🎉 This PR is included in version 10.24.2 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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