Move shared `aamtest` and `wdspec` infrastructure to shared directory in `tools`

[spectranaut]

The aamtests use some of the infrastructure fixtures defined in webdriver/tests/support.

Probably the fixtures shared between these two test types should be moved to tools so that it is more clear changes will effect both test types.

[spectranaut]

The current PR uses the following fixtures:

From webdriver/tests/support/fixtures.py:

• capabilities - used directly by aamtests
• full_configuration - used directly by aamtests
• inline - used directly by aamtests
• request - dependency of capabilities
• default_capabilities - dependency of capabilities
• server_config - dependency of inline
• url - dependency of inline
• configuration - dependency of classic session

From webdriver/tests/support/classic/fixtures.py:

• session - used directly by aamtests

From webdriver/tests/support/classic/helpers.py:

• cleanup_session - dependency of session

Some thoughts about the future:

Many aamtests will be very simple, just loading some html and inspecting the accessibility API.
Eventually we will add more complicated tests that either javascript will execute or otherwise interact with the browser using webdriver, then we will listen for events or changes in the accessibility API. In this case it might be helpful to re-use some functions like def center_point(element) in webdriver/tests/support/classic/helpers.py.

Once bidi is fully supported in WebKit, then we probably would want to use bidi for testing more complicated scenarios, and some of the fixtures in webdriver/tests/support/bidi/fixtures.py look like they could be shared.