Change access to VList children to a wrapper

[WorldSEnder]

Description

Fixes #2654

As a response to the confusion in #2654, restrict mutable access to the children of a VList to a wrapper that takes care of recomputing fully_keyed automatically.

Checklist

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

[github-actions]

Visit the preview URL for this PR (updated for commit b700f2f):

https://yew-rs-api--pr2673-vlist-children-nnp8i8rr.web.app

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[github-actions]

Size Comparison

examples	master (KB)	pull request (KB)	diff (KB)	diff (%)
boids	172.770	172.770	0	0.000%
contexts	109.642	109.642	0	0.000%
counter	86.654	86.654	0	0.000%
counter_functional	87.305	87.305	0	0.000%
dyn_create_destroy_apps	89.800	89.800	0	0.000%
file_upload	102.620	102.620	0	0.000%
function_memory_game	167.354	167.354	0	0.000%
function_router	350.424	350.424	0	0.000%
function_todomvc	161.987	161.987	0	0.000%
futures	226.616	226.657	+0.041	+0.018%
game_of_life	107.539	107.539	0	0.000%
inner_html	83.687	83.687	0	0.000%
js_callback	112.869	112.869	0	0.000%
keyed_list	195.036	195.036	0	0.000%
mount_point	86.281	86.281	0	0.000%
nested_list	115.908	115.908	0	0.000%
node_refs	90.450	90.450	0	0.000%
password_strength	1539.232	1539.232	0	0.000%
portals	97.197	97.197	0	0.000%
router	319.468	319.468	0	0.000%
simple_ssr	494.013	494.013	0	0.000%
ssr_router	425.761	425.761	0	0.000%
suspense	110.522	110.522	0	0.000%
timer	89.361	89.361	0	0.000%
todomvc	143.053	143.053	0	0.000%
two_apps	87.286	87.286	0	0.000%
web_worker_fib	153.530	153.530	0	0.000%
webgl	87.375	87.375	0	0.000%

✅ None of the examples has changed their size significantly.

[hamza1311]

I believe it also fixes #1815

[WorldSEnder]

@hamza1311 I believe ChildrenRenderer is its own separate thing. But I also believe that could simply implement Deref and DerefMut by itself to solve the issue over there.

EDIT: will merge this tomorrow, when I had to time to consider #1815