This helps to keep the prelude small and less likely to conflict with
other crates.
- remove widgets module from prelude as the entire module can be just as
easily imported with `use ratatui::widgets::*;`
- move prelude module into its own file
- update examples to import widgets module instead of just prelude
- added several modules to prelude to make it possible to qualify
imports that collide with other types that have similar names
- merge `Style` and `StyleDiff` together. `Style` now is used to activate or deactivate certain
style rules not to overidden all of them.
- update all impacted widgets, examples and tests.
- Remove deny warnings in lib.rs. This allows easier iteration when developing
new features. The warnings will make the CI fails anyway on the clippy CI
stage.
- Run clippy on all targets (including tests and examples) and all features.
- Fail CI on clippy warnings.
