fix: vantResolver partial name

[miyukoarc]

VantResolver would make a mistake in generating component name
just like
VantButton: typeof import('vant/es')['tButton']
"vant/es/t-button/style/index" this file does not exist
maybe that can help

if (name.startsWith('Vant')) {
    const partialName = name.slice(4);
    return {
        /*... */
    };
}