Enhance PositionPanel: Add z-index control and position value adjustments

[yogeshbhutkar]

Fixes: #67873

What?

This PR adds the option to set top, bottom, left, and right values along with the z-index when the position of a block is set to sticky.

Why?

Currently, there's no way to add the z-index and directional values which limits the capabilities of the block editor and emphasizes on the usage of Custom CSS to achieve the result. This has been properly described in the issue tagged above.

How?

The PR adds the required Block Controls for z-index and position values.

Testing Instructions

1. Insert a Group block.
2. Notice the z-index and directional options inside the position inspector controls.

Screenshots

Before	After

Screencast

1080p.mov

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