Amplify backend actions for webviews

[drkameleon]

Description

Right now, one of the different "access points" we have, so that our webviews communicate with the Arturo are backend actions. That is: named, function-like calls, available exclusively in this context (Webview <-> Arturo message passing) and are normally meant to offer system- or UI-specific functionality (e.g. "maximize the main window" ➡️ window.maximize).

Here, we'll attempt adding a few more of these actions and, thus, amplify a bit the spectrum of what can be done/accessed through the webview itself! 😉

Type of change

• Code cleanup
• Enhancement (implementation update, or general performance enhancements)
• New feature (non-breaking change which adds functionality)

[drkameleon]

Rough draft of what I'm thinking about a possible Window implementation (that's gonna be internal!):
and using our new... .safe getters/setters... #1821

(EDIT: This has been over-simplified in the end, but still following the idea of an "internal" custom type)

define :window [
    _isVisible: true
    _isFullscreen: false
    _isMaximized: false
    _title: ""
    
    ; placeholders
    _show: function [][]
    _hide: function [][]
    _fullscreen: function [][]
    _unfullscreen: function [][]
    _maximize: function [][]
    _unmaximize: function [][]
    _settitle: function [title][]
    
    close: function [][]
    evaluate: function [code][]

    get: method [what][
        case what [
            'visible?       -> return get.safe this '_isVisible
            'fullscreen?    -> return get.safe this '_isFullscreen
            'maximized?     -> return get.safe this '_isMaximized
            'title          -> return get.safe this '_title
            any             -> throw "Unrecognized field"
        ]
    ]

    set: method [what, value][
        case what [
            'visible?       [
                set.safe this '_isVisible value
                (value)? -> \show
                         -> \hide
            ]
            'fullscreen?    [
                set.safe this '_isFullscreen value
                (value)? -> \fullscreen
                         -> \unfullscreen
            ]
            'maximized?    [
                set.safe this '_isMaximized value
                (value)? -> \maximize
                         -> \unmaximize
            ]
            'title          [
                set.safe this '_title value
                \settitle value
            ]
        ]
    ]
]