Rewrite testing code to a TestRunner managing dom context

[WorldSEnder]

Description

Introduces a TestRunner that can mounts components, wait until they are done rendering, offers an API to test some properties about them and avoids mistakenly rendering over other running tests (should enable parallel testing, but this isn't yet available in the browser).

Also gets rid of the timeout based version of waiting for events to complete, by abstracting it with a TriggerBus (basically a global boolean flag that is used as the condition whether to suspend, or to await it until it turns "active"/true). Naming up for debate, feel free to bike-shed a bit, I'm not too keen on the name.

Fixes the failures of this form: https://github.com/yewstack/yew/runs/6289299836?check_suite_focus=true that appear from time to time due a slow browser. See also #2609 (comment)

Net negative code size

Checklist

• I have reviewed my own code
• I have rewritten tests
• Have to investigate the size increase, this should not have an impact on non-test code

[github-actions]

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[github-actions]

Size Comparison

Details

examples	master (KB)	pull request (KB)	diff (KB)	diff (%)
boids	172.765	173.890	+1.125	+0.651%
contexts	109.643	110.607	+0.965	+0.880%
counter	86.651	88.944	+2.293	+2.646%
counter_functional	87.302	89.553	+2.251	+2.578%
dyn_create_destroy_apps	89.798	92.910	+3.112	+3.466%
file_upload	102.620	104.906	+2.286	+2.228%
function_memory_game	167.348	168.316	+0.969	+0.579%
function_router	350.592	351.926	+1.334	+0.380%
function_todomvc	161.993	162.958	+0.965	+0.596%
futures	226.658	228.941	+2.283	+1.007%
game_of_life	107.510	109.815	+2.306	+2.145%
inner_html	83.685	85.916	+2.231	+2.666%
js_callback	112.878	113.850	+0.972	+0.861%
keyed_list	195.034	196.345	+1.311	+0.672%
mount_point	86.281	88.594	+2.312	+2.680%
nested_list	115.920	117.089	+1.169	+1.008%
node_refs	90.449	91.745	+1.296	+1.433%
password_strength	1539.199	1540.506	+1.307	+0.085%
portals	97.193	98.277	+1.084	+1.115%
router	319.632	320.451	+0.819	+0.256%
simple_ssr	494.018	494.018	0	0.000%
ssr_router	425.589	425.589	0	0.000%
suspense	110.581	111.545	+0.964	+0.872%
timer	89.362	91.652	+2.290	+2.563%
todomvc	143.053	145.353	+2.300	+1.608%
two_apps	87.286	89.594	+2.308	+2.644%
web_worker_fib	153.531	155.907	+2.376	+1.548%
webgl	87.373	89.657	+2.284	+2.614%

⚠️ The following examples have changed their size significantly:

examples	master (KB)	pull request (KB)	diff (KB)	diff (%)
counter	86.651	88.944	+2.293	+2.646%
counter_functional	87.302	89.553	+2.251	+2.578%
dyn_create_destroy_apps	89.798	92.910	+3.112	+3.466%
file_upload	102.620	104.906	+2.286	+2.228%
futures	226.658	228.941	+2.283	+1.007%
game_of_life	107.510	109.815	+2.306	+2.145%
inner_html	83.685	85.916	+2.231	+2.666%
mount_point	86.281	88.594	+2.312	+2.680%
nested_list	115.920	117.089	+1.169	+1.008%
node_refs	90.449	91.745	+1.296	+1.433%
portals	97.193	98.277	+1.084	+1.115%
timer	89.362	91.652	+2.290	+2.563%
todomvc	143.053	145.353	+2.300	+1.608%
two_apps	87.286	89.594	+2.308	+2.644%
web_worker_fib	153.531	155.907	+2.376	+1.548%
webgl	87.373	89.657	+2.284	+2.614%