Formula signature + doc improvements

[dej611]

Summary

This PR improves the signature popover while hovering and while typing.
Also the documentation has been increased - probably requires to check the compatibility with #13 that I just saw 😓 -.

• Adds more info about types/optionality in the function signature
• Refactor + centralize logic for hover + suggestion and doc in few functions
• Auto-generate examples based on arguments
• Fixed few math documentation informations that were wrong
• Adds and fix some more ES function parameters

I've seen there's a specific component in EUI for markdown, but originally it was using another Markdown component. Which one should be the final one?

for

mul

a

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

• This was checked for cross-browser compatibility, including a check against IE11
• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[wylieconlon]

@dej611 Merged this PR