Replace deprecated ReactDOM methods in Context Menu Singleton

[ggdouglas]

Tracking work required for full compatibility with React 18. The imperative API methods of Context Menu Popover (showContextMenu and hideContextMenu) expose DOMMountOptions that reference deprecated ReactDOM.render and ReactDOM.unmountComponentAtNode methods as option defaults. We should replace these defaults with the current root.render(...) and root.unmount() methods. This issue is similar/related to #7166

Current support for React 18 is achieved by passing in the new ReactDOM methods as options. From the docs:

"(or ReactDOM.createRoot() if you override the default renderer via options)"

Code:

contextMenuSingleton.tsx

blueprint/packages/core/src/components/context-menu/contextMenuSingleton.tsx

Lines 53 to 54 in ee5510c

	domRenderer = ReactDOM.render,
	domUnmounter = ReactDOM.unmountComponentAtNode,

blueprint/packages/core/src/components/context-menu/contextMenuSingleton.tsx

Line 84 in ee5510c

const { domUnmounter = ReactDOM.unmountComponentAtNode } = options;

References:

1. https://react.dev/blog/2022/03/08/react-18-upgrade-guide#updates-to-client-rendering-apis
2. Replacing render with createRoot reactwg/react-18#5

[ggdouglas]

For the initial internal React 18 upgrade, these deprecations will need to be ignored to pass the linter: #7159