…move TopBottomSide

NOTE: Non-working commit

…ethods

NOTE: Non-working commit

NOTE: Non-working commit

following those steps:
1. Rename `egui::SidePanel` with `egui::Panel`.
2. Rename `width` with `size` in all chained methods.
    - `default_width()` to `default_size()`
    - `min_width()` to `min_size()`
    - `max_width()` to `max_size()`
    - `width_range()` to `size_range()`
    - `exact_width()` to `exact_size()`

if using `Panel::new()`, replace
- `Side::Left` with `Side::Vertical(VerticalSide::Left)`
- `Side::Right` with `Side::Vertical(VerticalSide::Right)`

NOTE: Non-working commit

…pBottomPanel when both SidePanel and TopBottomPanel were mentioned.

following those steps:
1. Rename `egui::TopBottomPanel` with `egui::Panel`.
2. Rename `height` with `size` in all chained methods.
    - `default_height()` to `default_size()`
    - `min_height()` to `min_size()`
    - `max_height()` to `max_size()`
    - `height_range()` to `size_range()`
    - `exact_height()` to `exact_size()`

if using `Panel::new()`, replace
- `TopBottomSide::Top` with `Side::Horizontal(HorizontalSide::Top)`
- `TopBottomSide::Bottom` with `Side::Horizontal(HorizontalSide::Bottom)`

NOTE: Non-working commit

- replace switch fn with closures in some places.
- integrate the switch fn inside the main switch.
- make sure lifetime are defined for PanelSizer.
- remove some `mut`, `&`, and `*` where they superfluous.
- wrongly called `ctx()` when it was a variable 🤦.
- cannot use `impl Trait` in a variable declaration type.