Toolbar: Add input bindings for updateActionButton and updateSelectInput

[elnelson575]

Current usage of the input bindings doesn't permit updateActionButton to function properly and does not work at all for updateSelectInput.

We should fix this so these work well in toolbars.
Start with the button
Model the bindings on taskInputbutton:
taskButton.ts
need a find scope input binding (find in taskButton.ts)
getValue to get the value that needs to be sent to shiny
subscribe is where register eventListeners,
call 'callback' whenever the value changes
receiveMessage is what takes updates from shiny and reflects them on the UI (messages sent from session$sendInputMessage)

Decision Log:

• Do we need processDeps called on the inputs here like shiny?
• Should we add something like fa-fw (fixed-width) class (a Font Awesome utility to keep the width the same even when the icon size changes) to deal with updating icons and keeping button size the same?

[gadenbuie]

Examples for reference:

https://github.com/rstudio/shiny/blob/fda6a9fede967fce46050f540612bb501e18f673/R/update-input.R#L661-L675

A modern example from bslib, where label is _definitely` text:

bslib/R/input-switch.R

Lines 62 to 70 in 0757592

	update_switch <- function(
	id,
	label = NULL,
	value = NULL,
	session = get_current_session()
	) {
	message <- dropNulls(list(label = label, value = value))
	session$sendInputMessage(id, message)
	}

Another modern example with HTML content:

bslib/R/popover.R

Lines 179 to 200 in 0757592

	update_popover <- function(
	id,
	...,
	title = NULL,
	session = get_current_session()
	) {
	body <- tagList(...)
	msg <- dropNulls(
	list(
	method = "update",
	content = if (length(body) > 0) processDeps(body, session),
	header = if (!is.null(title)) processDeps(title, session)
	)
	)
	force(id)
	callback <- function() {
	session$sendInputMessage(id, msg)
	}
	session$onFlush(callback, once = TRUE)
	}