fix(overlays): assign incremental id to overlay host

[sean-perkins]

Issue number: Internal

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What is the current behavior?

The counter for incrementing the id and z-index of an overlay is incremented whenever the connectedCallback is fired for an overlay.

When an overlay is presented and/or conditionally rendered, the overlay id can increment by n+2 instead of n+1.

What is the new behavior?

• Increments all overlay ids consistently
• Removes legacy ion-modal-{id} and ion-popover-{id} logic
• Adds unit tests for the id behavior
  • Tests are split up into separate files so that the counter is always starting from 0
• Adds an integration test with the Angular test app to verify conditional rendering behavior

Does this introduce a breaking change?

• Yes
• No

Other information

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[sean-perkins]

Let me know if anyone else feels like a fixture would be useful here for the repeat overlay tests.

[liamdebeasi]

Good to go after the two comments are addressed.