feat(util): add `callbackify` & `promisify`

[MichaelDeBoey]

Just like @IvanKushchenko did in https://github.com/ionic-team/rollup-plugin-node-polyfills/pull/40 & @abhishek-mittal did in https://github.com/ionic-team/rollup-plugin-node-polyfills/pull/45

@giuseppeg suggested in https://github.com/remorses/esbuild-plugins/pull/19#discussion_r1048398962 to use https://github.com/browserify/node-util directly, but we can do that in a follow-up PR if that's OK for @FredKSchott

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Closes https://github.com/ionic-team/rollup-plugin-node-polyfills/issues/38

[MichaelDeBoey]

@FredKSchott Do I need to do anything else to get this one merged?

[FredKSchott]

LGTM!