Improve nav_*() and navset_*() function names

[gadenbuie]

For #476

Overview

This is a big, wide-ranging PR with simple naming changes. There are two over-arching goals:

1. Improve the names of nav-item functions, in particular to make nav() more descriptive.
2. Create a better separation between navs_ and nav_ prefixes by replacing the first with navset_.

API Changes

Here's a short summary of the changes. In all cases, deprecation warnings are emitted unless the functions are called from Shiny (to give us time to migrate the changes where bslib::nav() and others are called directly).

New	Old	Shiny equiv	Notes
nav_panel()	nav()	tabPanel()
nav_panel_hidden()	nav_content()	tabPanelBody()	1
navset_tab()	navs_tab()	tabsetPanel()
navset_pill()	navs_pill()	tabsetPanel(type="pill")
navset_pill_list()	navs_pill_list()	navlistPanel()
navset_hidden()	navs_hidden()	tabSetPanel(type="hidden")	1
navset_bar()	navs_bar()	pageNavbar() adjacent?
navset_card_tab()	navs_tab_card()	(none)	2
navset_card_pill()	navs_pill_card()	(none)	2

In the revised API, all functions starting with navset_*() take items prefixed with nav_().

Notes:

1. nav_content() is now nav_panel_hidden() (which pairs with navset_hidden()). The panel itself isn't hidden necessarily; the hidden refers to the fact that there isn't a <nav> container with controls (e.g. a wizard interface).
2. The _card part of the function name was moved in front of tab|pill in navset_card_tab() and navset_card_pill() to reflect that card is higher priority in usage.

PR Notes

There's a lot of work in flight in the bslib articles, so I only made changes in the R functions, documentation, and examples. We can wait for those PRs to land or we can tackle those updates in a follow-up PR. Update: this is done now.

I also took care to ensure that the aliased functions appear at the end of any function lists in the documentation. All aliases are now collected in R/navs-aliases.R with TODO items so we can deprecate them in future version of bslib. Update: these functions will be formally deprecated.

I marked the deprecated functions as "renamed in v0.5.0". We're currently on v0.4.2.9000 and I'm assuming, from looking at our current NEWS situation that we'd be doing a minor version bump with the next release.

Remaining work

Need to:

• Clean up navset example images and ensure correct naming.
• Update usage in bslib's articles.

For discussion or possibly a future PR:

• Also rename nav_item()? In Shiny for Python this became nav_control().
• Rename fillable in page_navbar() to fillable_panel?

[gadenbuie]

Oops, I thought I merged main into this branch before updating the articles. I'll finish this up early next week.

[nstrayer]

I think this is much easier to understand!

[jcheng5]

Looks a lot better to me too

[gadenbuie]

Python API

Comparing the new names with the current Shiny for Python API:

bslib (new)	Python (current)	Changes?
nav_panel()	ui.nav	👀
nav_panel_hidden()	ui.nav_content	👀 ❗
navset_tab()	ui.navset_tab
navset_pill()	ui.navset_pill
navset_pill_list()	ui.navset_pill_list
navset_hidden()	ui.navset_hidden	❗
navset_bar()	ui.navset_bar	❗
navset_card_tab()	ui.navset_tab_card	👀
navset_card_pill()	ui.navset_pill_card	👀

👀 new R name is different from current Python
❗ not in API refs