fix(react): declare DefinitionTooltip's children prop as required (#19938)

Declare `DefinitionTooltip`'s `children` prop as non-nullable in
TypeScript to match the PropTypes `isRequired` definition, which is
the correct one per Nikhil Tomar [1].

Fixes #19834.

[1] #19834 (comment)

Author: nchevsky

packages/react/src/components/Tooltip/DefinitionTooltip.tsx

@@ -34,7 +34,7 @@ export interface DefinitionTooltipProps
   /**
    * The `children` prop will be used as the value that is being defined
    */
-  children?: React.ReactNode;
+  children: React.ReactNode;
 
   /**
    * Specify an optional className to be applied to the container node