fix(ol-webgl-tile-layer): react on property changes

[d-koppenhagen]

• make TileLayer a shallowRef, to not always create a new class
• apply property changes using .set('<prop>', value)
• add demo for opacity / visibility changes

closes #319

Description

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of Changes

• [x] Bug fix (non-breaking change that fixes an issue)
• [ ] New feature (non-breaking change that adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] Documentation Update
• [ ] Tests
• [ ] Other (Tooling, Dependency Updates, etc.)

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I added a new test.

If you added a new component feature (layer, geom, source, etc.), please be sure to update the documentation:

• [ ] Add component to output.globals in vite.config.ts
• [ ] Provide at least one simple snapshot test (see test directory)
• [ ] Create a src/demos/<Component>Demo.vue
• [ ] Create a docs/componentsguide/<Category>/<Feature>/index.md containing the Demo and documentation for the component
• [ ] Add the docs page to docs/.vitepress/config.ts

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