FormTokenField: Validate input before tokenizing on space

[dhruvikpatel18]

Closes #69252

What?

This PR fixes the FormTokenField component to properly validate input before creating tokens when pressing the space key.

Why?

Currently, when the tokenizeOnSpace prop is enabled, the FormTokenField component creates tokens immediately on space press without checking the experimentalValidateInput function. This can lead to invalid tokens being created, which is inconsistent with the validation behavior when using other methods of token creation (like pressing Enter or comma).

How?

Modified the space key handler in the onKeyDown function to:

1. Check if there's valid input using inputHasValidValue()
2. Call experimentalValidateInput with the current value
3. Only create a token if both checks pass

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Co-authored-by: dhruvikpatel18 <[email protected]>
Co-authored-by: alshakero <[email protected]>

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