Consider deprecating HTML in Selectize Labels

[elnelson575]

After our next release and accompanying deprecation warning, we should consider changing update_selectize to change label = v and label = v2, which will switch the Mapping[str, TagChild] to Mapping[str, str]

(See: #1947 for related issue/fix)

We should instead provide an example for how to customize html with the options field once we remove the ability to pass in HTML into labels.

@cpsievert per our discussion, feel free to update/edit.

[cpsievert]

After some further investigation, I think we can just go ahead and make that change now (in this release). I don't think HTML choice labels have ever worked for input_select() or input_selectize(), and I don't think it's even a sensibly feasible thing to do with select or selectize.js.

Here's a minimal example where the current behavior clearly isn't right.

from shiny import reactive
from shiny.express import ui

ui.input_selectize(
    "foo",
    None,
    choices=[],
    multiple=True,
)

@reactive.effect
def _():
    ui.update_selectize(
        "foo",
        choices={f"Foo & {i}": ui.tags.b(f"Foo & {i}") for i in range(10000)},
        selected=["Foo & 0", "Foo & 1"],
        server=True,
    )

In addition to removing the _process_ui calls in update_selectize(), let's also go ahead and:

1. Change _Choices = Mapping[str, TagChild] -> _Choices = Mapping[str, str].
2. Drop the deprecation message from fix(input_select): Decouple input_select() and input_selectize() #1947 (the new type errors will be enough)
3. Update the changelog accordingly (mentioning that this was never a thing that actually worked)
   • If we want to be nice, we could mention options.render as a way to customize the HTML rendering of labels/items