Refactor number input foundation

[agluszak]

Summary

• Move typed numeric text editing into headless bevy_ui_widgets::NumberInput
• Add the bounded RangedNumberInput foundation and Feathers wrapper
• Keep Feathers number_input as a styled numeric text input without spinbox controls
• Add the Feathers gallery alpha ranged number input example

Validation

• cargo test -p bevy_ui_widgets number_input
• cargo test -p bevy_ui_widgets ranged_number_input
• cargo test -p bevy_feathers
• cargo check -p bevy --example feathers_gallery --features experimental_bevy_feathers

[alice-i-cecile]

Related to #24060.