Allow VNode props to be converted to Children.

[futursolo]

Description

Fixes #1744

Checklist

• I have reviewed my own code
• I have added tests

[github-actions]

Visit the preview URL for this PR (updated for commit 544ad8c):

https://yew-rs-api--pr2749-vnode-children-vxbq7x5l.web.app

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[github-actions]

Size Comparison

examples	master (KB)	pull request (KB)	diff (KB)	diff (%)
boids	172.593	172.593	0	0.000%
contexts	109.620	109.620	0	0.000%
counter	86.550	86.550	0	0.000%
counter_functional	87.203	87.203	0	0.000%
dyn_create_destroy_apps	89.664	89.664	0	0.000%
file_upload	102.626	102.626	0	0.000%
function_memory_game	166.894	166.894	0	0.000%
function_router	351.665	351.666	+0.001	+0.000%
function_todomvc	161.561	161.561	0	0.000%
futures	226.233	226.233	0	0.000%
game_of_life	107.189	107.189	0	0.000%
inner_html	83.618	83.618	0	0.000%
js_callback	112.846	112.846	0	0.000%
keyed_list	195.105	195.105	0	0.000%
mount_point	86.180	86.180	0	0.000%
nested_list	115.688	115.688	0	0.000%
node_refs	93.597	93.597	0	0.000%
password_strength	1538.157	1538.157	0	0.000%
portals	97.225	97.225	0	0.000%
router	320.458	320.458	0	0.000%
simple_ssr	154.493	154.493	0	0.000%
ssr_router	398.062	398.062	0	0.000%
suspense	110.544	110.544	0	0.000%
timer	89.258	89.258	0	0.000%
todomvc	142.615	142.615	0	0.000%
two_apps	87.160	87.160	0	0.000%
web_worker_fib	153.406	153.406	0	0.000%
webgl	87.438	87.438	0	0.000%

✅ None of the examples has changed their size significantly.