docs(cdk/coercion): add guidance on Angular built-in input transforms

[yogeshwaran-c]

What kind of change does this PR introduce?

Documentation improvement

What is the current behavior?

The CDK coercion documentation only shows the legacy pattern of using
coerceBooleanProperty and coerceNumberProperty with @Input() getters
and setters. It does not mention that Angular now provides built-in equivalents
(booleanAttribute and numberAttribute) that work with signal inputs.

Closes #27718

What is the new behavior?

Updates the coercion documentation to:

• Add a comparison table showing CDK coercion functions and their Angular
  built-in equivalents (booleanAttribute, numberAttribute)
• Recommend Angular's built-in transforms with signal inputs for new code
• Show a modern example using input() with {transform: booleanAttribute}
  and {transform: numberAttribute}
• Note that CDK-specific functions like coerceElement and coerceArray
  remain useful for custom coercion logic
• Modernize the example code to use signal inputs

Additional context

Since Angular v16+, the transform option on @Input() made CDK coercion
less necessary for boolean and number inputs. Since Angular v17+, signal inputs
(input()) with transforms provide the cleanest API. The CDK coercion module
is still useful for coerceElement, coerceArray, and custom coercion logic.