fix(language-plugin-pug): should cache proxyed object

[kermanx]

fix #4335.

This PR caches proxyed objects created by the Pug plugin, so that logic involving equality checking would work.

Previously, the following line doesn't remove v-for node because every time node.props generates a different array.

language-tools/packages/language-core/lib/codegen/template/templateChild.ts

Line 138 in 9ef235b

props: node.props.filter(prop => prop !== forDirective),

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[johnsoncodehk]

LGTM, thanks!