sokol_app.h html5: event bubbling followup fixes...

[floooh]

The recent fix to simply let bubble mouse and touch events up to the web page has some undesirable side effects:

• Dear ImGui touch input broken on mobile browsers #969
• on the standard samples, double- and triple-clicking into the canvas will select the overlay HTML text (e.g. https://floooh.github.io/sokol-html5/clear-sapp.html)

Related:

• Optionally capturing keyboard input in web app #800
• app: add JS function to enable/disable capturing canvas keyboard events #801
• comment in favour of this idea: - sokol_app: EMSCRIPTEN: can't write into a textarea while sapp is running #822 (comment)

Solution: restore previous default behaviour (mouse, touch and maybe key input does not bubble up by default), and instead add the following config items to sapp_desc:

• html5_bubble_mouse_events
• html5_bubble_wheel_events
• html5_bubble_touch_events
• html5_bubble_key_events
• html5_bubble_char_events

...this would be a good opportunity (but a breaking change) to introduce nesting for those platform-specific config items, e.g. (still a good idea, but for a later time)

return (sapp_desc){
    .win32 = {
        ...
    },
    .html5 = {
        ...
    }
};

[floooh]

Fixed via #975