refactor: cleanup

[mlmoravek]

Last cleanup for the switch to composition api.

Fixes #606

Proposed Changes

• Updated several slot/prop descriptions
• Add code comments
• Extract programmatic functional to specific files
• Add associated type definition files
• Remove unused files

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[codecov]

Codecov Report

Attention: 9 lines in your changes are missing coverage. Please review.

Comparison is base (239ad99) 58.77% compared to head (37711e5) 58.45%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #651      +/-   ##
===========================================
- Coverage    58.77%   58.45%   -0.32%     
===========================================
  Files           87       89       +2     
  Lines         2428     2448      +20     
  Branches       818      819       +1     
===========================================
+ Hits          1427     1431       +4     
- Misses         890      906      +16     
  Partials       111      111              

Flag	Coverage Δ
oruga	67.21% <ø> (ø)
oruga-next	47.77% <47.05%> (-0.52%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...ckages/oruga-next/src/components/button/Button.vue	82.60% <ø> (ø)
...es/oruga-next/src/components/checkbox/Checkbox.vue	86.36% <ø> (ø)
...es/oruga-next/src/components/collapse/Collapse.vue	100.00% <ø> (ø)
...ckages/oruga-next/src/composables/useClassProps.ts	100.00% <100.00%> (ø)
packages/oruga-next/src/utils/config.ts	62.50% <ø> (+1.38%)	⬆️
packages/oruga-next/src/components/field/Field.vue	78.12% <0.00%> (-1.88%)	⬇️
packages/oruga-next/src/utils/helpers.ts	11.62% <0.00%> (ø)
packages/oruga-next/src/utils/plugins.ts	26.66% <33.33%> (ø)
...-next/src/components/autocomplete/Autocomplete.vue	53.99% <60.00%> (+0.12%)	⬆️

... and 1 file with indirect coverage changes

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