feat(api(session)): Start process of making session arguments removed from API

[schloerke]

Related to #790

• Update session to have type MISSING_TYPE in functions where it could be resolved by using with session_context(sess):
• Remove @output and session from server definitions in examples (where possible)

• Changelog entry

App examples

Before:

from shiny import App, Inputs, Outputs, Session, reactive, render, ui

app_ui = ui.page_fluid(
    ui.input_slider("controller", "Controller", min=0, max=1, value=0, step=1),
    ui.input_checkbox("inCheckbox", "Input checkbox"),
    ui.output_text_verbatim("txt", placeholder = True),
)


def server(input: Inputs, output: Outputs, session: Session):
    @reactive.Effect
    def _():
        # True if controller is odd, False if even.
        x_even = input.controller() % 2 == 1
        ui.update_checkbox("inCheckbox", value=x_even)

    @output
    @render.text
    def txt():
        return str(input.controller())

app = App(app_ui, server)

After:

from shiny import App, Inputs, reactive, render, ui

app_ui = ui.page_fluid(
    ui.input_slider("controller", "Controller", min=0, max=1, value=0, step=1),
    ui.input_checkbox("inCheckbox", "Input checkbox"),
    ui.output_text_verbatim("txt", placeholder=True),
)


def server(input: Inputs):
    @reactive.Effect
    def _():
        # True if controller is odd, False if even.
        x_even = input.controller() % 2 == 1
        ui.update_checkbox("inCheckbox", value=x_even)

    @render.text
    def txt():
        return str(input.controller())


app = App(app_ui, server)