web renderer: support UTF-8 input

[zpl-zak]

see:

• https://github.com/ultralight-ux/Ultralight/blob/208d653e872b29234bbd4a5fef6dec403f3dfdbd/samples/Sample%207%20-%20OpenGL%20Integration/src/Window.cpp#L39
• https://gist.github.com/matias-eduardo/7804347beae42a62393db1c38f46c70d

[zpl-zak]

https://stackoverflow.com/questions/75191880/windows-producing-utf8-sequence-for-ansi-version-wm-char-why-i-cannot-see-it?rq=2

[zpl-zak]

partially handled by 0c6053c...abc6bf0