Warehouse Robot Collection

Imagine a warehouse represented as a 2D grid of characters. The grid is given as an array of strings, where each character represents a cell in the warehouse:

• S: the starting position of the robot (appears exactly once)
• D: the destination point (appears exactly once)
• I: an item that must be collected (there can be zero or more items)
• .: an empty space where the robot can move freely
• X: an obstacle that cannot be traversed

The robot can move up, down, left, or right, and each move counts as one step. The robot must collect all items (cells marked with I) before reaching the destination D.

Write a function that, given the warehouse grid, returns the minimum number of steps required for the robot to collect all items and reach the destination. If it is not possible to complete the task, return -1.

Assume that the grid size is moderate (e.g., up to 20x20), which allows an exhaustive search approach if necessary.