dcc redesign: refactor `Loading` component #438

Job	Run time
Detect Relevant Path Changes	5s
Build Dash Package	3m 19s
Run Background & Async Callback Tests (Python ${{ matrix.python-version }})	0s
Typing Tests	2m 45s
Table Unit/Lint Tests (Python ${{ matrix.python-version }})	0s
Table Server Tests (Group ${{ matrix.test-group }})	-1s
	6m 8s

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