Change access modifiers for Tabs methods to be more extensible

### Code of conduct

- [x] I agree to follow this project's code of conduct.

### Description of issue

We would like to access more parent properties and methods in Tabs from child classes:

- https://github.com/adobe/spectrum-web-components/blob/main/packages/tabs/src/Tabs.ts#L303
- https://github.com/adobe/spectrum-web-components/blob/main/packages/tabs/src/Tabs.ts#L181
- https://github.com/adobe/spectrum-web-components/blob/main/packages/tabs/src/Tabs.ts#L164
- https://github.com/adobe/spectrum-web-components/blob/main/packages/tabs/src/TabsOverflow.ts#L104

Start by inspecting the referenced declarations in packages/tabs/src/Tabs.ts at lines 164, 181, and 303, plus packages/tabs/src/TabsOverflow.ts at line 104. Determine which parent properties and methods child classes need to access, then verify that the resulting visibility changes support extension without breaking existing behavior.

Written by the indexing model from the issue text.