[InputGroup] Refactor API to extend HTMLInputProps

[cmslewis]

We should refactor IInputGroupProps to extend from HTMLInputProps, so that users can add custom callbacks on focus, on blur, and so on. The problem at present is that IInputGroupProps already extends from IControlledProps, which exposes props that conflict with some of those also included in HTMLInputProps (in particular: onChange, defaultValue, and value). Here's the exact set of errors you see:

[ts]
Interface 'IInputGroupProps' cannot simultaneously extend types 'IControlledProps' and 'HTMLProps<HTMLInputElement>'.
  Named property 'defaultValue' of types 'IControlledProps' and 'HTMLProps<HTMLInputElement>' 
  are not identical.

[ts]
Interface 'IInputGroupProps' cannot simultaneously extend types 'IControlledProps' and 'HTMLProps<HTMLInputElement>'.
  Named property 'onChange' of types 'IControlledProps' and 'HTMLProps<HTMLInputElement>' are 
  not identical.

[ts]
Interface 'IInputGroupProps' cannot simultaneously extend types 'IControlledProps' and 'HTMLProps<HTMLInputElement>'.
  Named property 'value' of types 'IControlledProps' and 'HTMLProps<HTMLInputElement>' are not 
  identical.

EDIT: There may be a better way to achieve this; the goal is primarily to expose the HTML Input lifecycle callbacks somehow.

[giladgray]

i wonder about adding something like htmlProps as a generic way for Blueprint components to support arbitrary spreads?

[cmslewis]

^ Definitely think that's worth exploring.

[llorca]

in the React types, we use HTMLProps, but there's also HTMLAttributes (HTMLProps minus the React attributes). We should probably always use HTMLAttributes