fix(types): allow null for line chart point values (#12027)

[anshukushwaha07]

This PR updates the TypeScript definition for Point to allow null values for x and y.

According to the Chart.js documentation, null is valid for skipped values in line charts. However, the current typings only accept number, which causes TypeScript errors when using null in datasets.

Before

export interface Point {
  x: number;
  y: number;
 }

After

export interface Point {
  x: number | null;
  y: number | null;
}

Example

new Chart<'line'>(ctx, {
  type: 'line',
  data: {
    datasets: [
      {
        data: [
          { x: 10, y: 20 },
          { x: 15, y: null }, //  now type checks correctly
          { x: 20, y: 10 }
        ]
      }
    ]
  }
});

Why this change is needed

• Runtime behavior already supports null (point is skipped).
• Docs confirm null is valid.
• TypeScript definitions should align with runtime and docs.
• Fixes TypeScript error: Type 'null' is not assignable to type 'number'

[anshukushwaha07]

Thanks @LeeLenaleee , I’ve applied the suggested changes. Please re-review.