Update strip component to new theming system

[bartaz]

Done

• Updates strips to use new theming system with is-light is-dark is-paper class names.
• Introduces new p-strip--highlighted to replace a variety of strip colour variants with a single themed version of a strip with an alternative backround colour
• Deprecates a number of old strips that are not meant for new designs: p-strip--dark p-strip--light p-strip--white p-strip--image p-strip--suru, etc. They should be replaced by new themed versions.
• Updates all the necessary docs and examples.

Fixes WD-8473

QA

• Open demo
• Check the dark strip example: https://vanilla-framework-4996.demos.haus/docs/examples/patterns/strips/dark
  • verify in inspector that it takes colors from CSS variables
  • change the theme to is-light, is-paper to check if it adjusts
• Check the highlighted strip example: https://vanilla-framework-4996.demos.haus/docs/examples/patterns/strips/highlighted
  • change the theme class (on body or on strip)
  • make sure the colour changes: on dark theme it should use a "lighter" dark, on paper it should use white, on light it should use light grey
• Verify that old deprecated versions are still supported
  • white
  • suru
  • light
  • dark
  • bordered
  • image
  • accent
• Review updated documentation:
  • https://vanilla-framework-4996.demos.haus/docs/patterns/strip

Check if PR is ready for release

If this PR contains Vanilla SCSS code changes, it should contain the following changes to make sure it's ready for the release:

• PR should have one of the following labels to automatically categorise it in release notes:
  • Feature 🎁, Breaking Change 💣, Bug 🐛, Documentation 📝, Maintenance 🔨.
• Vanilla version in package.json should be updated relative to the most recent release, following semver convention:
  • if CSS class names are not changed it can be bugfix relesase (x.x.X)
  • if CSS class names are changed/added/removed it should be minor version (x.X.0)
  • see the wiki for more details
• Any changes to component class names (new patterns, variants, removed or added features) should be listed on the what's new page.

Screenshots

[webteam-app]

Demo starting at https://vanilla-framework-4996.demos.haus

[britneywwc]

Everything looks good, just need some minor fixes mentioned in the comments

[britneywwc]

Looks great, thank you!

[lyubomir-popov]

Looks good, with a suggestion for the docs.

[lyubomir-popov]

Suggested change

	The strip component is rarely used on its own as a container with just `.p-strip` class name. It is usually combined with other variants described below to provide a specific visual style.
	Strips are containers that apply top/bottom padding and background colour. At a glance:
	- Strips come in 3 sizes - shallow, regular and deep. See details below.
	- They now support theming.
	- You can choose between regular (using the respective theme's background) or highlighted (Using each theme's alternative highlight colour).
	The strip component is rarely used on its own as a container with just `.p-strip` class name. It is usually combined with other variants described below to provide a specific visual style.

[bartaz]

Thanks, reworded a bit to fit better in current docs structure, but I added all of the information you mentioned.