Use instanced EventHub with ExtensionContainer

[timkimadobe]

Description

This PR updated the ExtenionContainer class to use an instance of EventHub instead of a shared global reference.

This is to avoid a relatively common test scenario where EventHub is started and shutdown rapidly between test cases, and extension containers have pending events that will get sent to the new EventHub instance; this can affect test case state, shared states, processing times, etc.

See: https://github.com/adobe/aepsdk-core-ios/issues/1064

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] I have signed the Adobe Open Source CLA.
• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.