Review dcc.Graph and move suitable tests to dcc repo #1031

Updating from plotly.js 1.51.1 to 1.51.2 caused https://github.com/plotly/dash/blob/dev/tests/integration/test_render.py#L974 to fail obscurely in the Dash repo.

• Review tests involving dcc.Graph: those that are not clearly testing a Dash/renderer behavior should be moved to dcc
• Review test content to make tests more resilient (e.g. in the example above we care about only some of the props, not all of them, nor the entire event structure -- that's for Plotly.js to test)