Normalize and improve font sizes

This commit standardizes font sizes across components for a uniform
look. The icon sizes, font weights and line heights are also adjusted
accordingly for better standardization and simplicity.

- Introduce variables for standard font sizes, enhancing
  maintainability.
- Remove explicit pixel values, replaced with scalable units based on
  root size.
- Remove workaround for line-height adoptation of bigger font-size.
- Use consistent small font-size for the code area.
- Adjust checkbox tick to scale with font size.

src/presentation/components/Scripts/Menu/Selector/SelectionTypeDocumentation.vue

@@ -101,9 +101,6 @@ ul {
   padding-left: 0em;
   margin-top: 0.25em;
   list-style: disc;
-  li {
-    line-height: 1.2em;
-  }
 }
 .sections {
   display: flex;