React 19 Compatibility: Remove `defaultProps` from Function Components

[ggdouglas]

React 19 removes support for defaultProps on function components in favor of ES6 default parameters. As stated in the React 19 Upgrade Guide:

We're also removing defaultProps from function components in place of ES6 default parameters. Class components will continue to support defaultProps since there is no ES6 alternative.

Blueprint currently has two functional components that use the deprecated defaultProps object: DateInput and Overlay2

blueprint/packages/datetime/src/components/date-input/dateInput.tsx

Lines 567 to 569 in 7668fd2

	// TODO: Removing `defaultProps` here breaks tests. Investigate why.
	// eslint-disable-next-line @typescript-eslint/no-deprecated
	DateInput.defaultProps = DATEINPUT_DEFAULT_PROPS;

blueprint/packages/core/src/components/overlay2/overlay2.tsx

Lines 657 to 658 in 7668fd2

	// eslint-disable-next-line @typescript-eslint/no-deprecated
	Overlay2.defaultProps = OVERLAY2_DEFAULT_PROPS;

We will remove defaultProps from these components and replace with ES6 default parameters. The following PRs capture this:

• [DateInput]: Remove defaultProps and consolidate datetime constants #7516
• [Overlay2]: Remove defaultProps from component #7517

Additionally, in the future when refactoring class components to function components, any instances of static defaultProps should also be replaced with ES6 default parameters.