Convert package interface to Typescript

[ws333]

It was challenging to split the rest into several PRs so here is the full conversion of package interface to typescript.

Some comments to the files added and important changes...

.prettierrc

• To keep the same code formatting as before

esling.config.mjs

• Copied from fresh vite react-ts project
• A few relevant rules added and set to warn
• There are two warnings for regexes in utils.ts and one warning in index.tsx about fast refresh that you can look at.

package.json

• Moved development dependencies under devDependencies

packages/iframe-service/src/iframe-service.ts

• Objects passed to messageChild did not match the type MessagePayload
• After fixing this I narrowed down the type of payload passed to messageChild, and also messageParent in packages/interface/src/service.ts.

The delay input will now be set to 0 instead of blank when using backspace to delete the numbers.

I refactored some of the runtime code like generatePrefUpdate in settings-tab.tsx, since now passing a constructed event value instead of an empty string in clearClicked onChange in the ClearableInput component in common.tsx.

I also changed all event.target to event.currentTarget since some HTML element types don't have an event.target.

Tested with both browser and Thunderbird and seems to work as expected.