feat: add WebView::load_html for loading HTML after intialization

[just-be-dev]

This PR aims to implement load_html, a companion of load_url to balance out the current implementation. Currently, the webview can be initialized with either a URL or HTML via .with_url or .with_html in the builder. After creation .load_url can be used to load a different URL, but the same can't be said for .load_html.

In #1367 I noted that refreshing a webview initialized with .load_html causes the webview to be left with an empty screen. While that's not ideal, if this method existed it'd be easy enough to simply call load_html with the same payload as what the webview was initialized with to get it back in the correct state.

[github-actions]

Package Changes Through 481a199

There are 1 changes which include wry with minor

Planned Package Versions

The following package releases are the planned based on the context of changes in this pull request.

package	current	next
wry	0.44.1	0.45.0

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[just-be-dev]

I've got a PR in my library that tests the code path for this PR: just-be-dev/webview#56. That's what I've used to test the implementation.

[just-be-dev]

I got someone at Recurse to verify that it works on windows as well. Still need to test on linux, but I'll get someone for that soon. My library isn't really setup to be ran on iOS or android so I'd appreciate extra scrutiny there. Overall the implementation seems straight forward though.

[amrbashir]

Thank you