[Bug] DrawAreaTask saves duplicate points and allows degenerate polygons

[shobhitagarwal1612]

Description

During a refactor of the DrawAreaTask state management to adhere to Unidirectional Data Flow (UDF) principles (#3678), several issues were identified in the polygon drawing logic that could lead to invalid geometry being saved and a confusing user experience.

Detected Issues

1. Duplicate Points in Storage: Incomplete polygons were saving duplicate points (specifically duplicating the last vertex), resulting in 4 points instead of 3 for a triangle.
2. Incorrect Undo Behavior: The Undo action would remove a committed vertex even when there was a tentative vertex actively being drawn on the screen.
3. Missing Validation for Degenerate Shapes: The proximity check (isTooClose) failed to trigger when closing a triangle with only 2 committed points, allowing degenerate lines to be formed.
4. Premature Button Visibility: The COMPLETE button was displayed for closed shapes that didn't have enough distinct points to form a valid polygon (requires 3 distinct points).

Proposed Fix

The implementation has been refactored in the current branch to:

• Separate committed vertices from the transient tentative vertex in the ViewModel state.
• Clear the tentative vertex upon commit.
• Enforce a minimum of 3 distinct points for closure validation.
• Update proximity checks to cover all edge cases when closing shapes.
• Introduce PolygonDrawingSession class to encapsulate list of committed vertices, transient tentative vertex, redo stack, operations like adding a vertex, undoing, and redoing.

Steps to Reproduce

1. Start drawing an area task.
2. Place 3 points.
3. Observe that the saved incomplete geometry contains 4 points instead of 3.