* feat(layout): add a Rect::clamp() method
This ensures a rectangle does not end up outside an area. This is useful
when you want to be able to dynamically move a rectangle around, but
keep it constrained to a certain area.
For example, this can be used to implement a draggable window that can
be moved around, but not outside the terminal window.
```rust
let window_area = Rect::new(state.x, state.y, 20, 20).clamp(area);
state.x = rect.x;
state.y = rect.y;
```
* refactor: use rstest to simplify clamp test
* fix: use rstest description instead of string
test layout::rect::tests::clamp::case_01_inside ... ok
test layout::rect::tests::clamp::case_02_up_left ... ok
test layout::rect::tests::clamp::case_04_up_right ... ok
test layout::rect::tests::clamp::case_05_left ... ok
test layout::rect::tests::clamp::case_03_up ... ok
test layout::rect::tests::clamp::case_06_right ... ok
test layout::rect::tests::clamp::case_07_down_left ... ok
test layout::rect::tests::clamp::case_08_down ... ok
test layout::rect::tests::clamp::case_09_down_right ... ok
test layout::rect::tests::clamp::case_10_too_wide ... ok
test layout::rect::tests::clamp::case_11_too_tall ... ok
test layout::rect::tests::clamp::case_12_too_large ... ok
* fix: less ambiguous docs for this / other rect
* fix: move rstest to dev deps
This method splits a Rect and returns a fixed-size array of the
resulting Rects. This allows the caller to use array destructuring
to get the individual Rects.
```rust
use Constraint::*;
let layout = &Layout::vertical([Length(1), Min(0)]);
let [top, main] = area.split(&layout);
```
The offset method creates a new Rect that is moved by the amount
specified in the x and y direction. These values can be positive or
negative. This is useful for manual layout tasks.
```rust
let rect = area.offset(Offset { x: 10, y -10 });
```
- add `Rect::is_empty()` that checks whether either height or width == 0
- refactored `Rect` into layout/rect.rs from layout.rs. No public API change as
the module is private and the type is re-exported under the `layout` module.
