bug(web): BuildVisualKeyboard issues

**Describe the bug**

1. `BuildVisualKeyboard` (ultimately `buildDocumentationKeyboard`) returns a malformed OSK if passed a non-existent layer; see https://github.com/keymanapp/help.keyman.com/issues/596 for examples.
2. `BuildVisualKeyboard` ignores the `static` parameter
3. Even if passed a specific layer, the function builds and returns all layers and simply marks one of them as visible -- which is definitely not optimal.
4. If the returned kbd element is never inserted into the DOM, the refreshInterval timer will run every 10msec until the page is closed.
5. `refreshLayout()` is called twice -- both before and after insertion into the DOM.
6. `getOskHeight()` hack needs to be addressed!

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**Keyman Engine for Web:**
Device: any
- OS: any
- Browser: any
- KeymanWeb Version: 15.0.269
- URL: https://help.keyman.com/keyboard/*