Support `content_for` block `closest.metaobject` param completion

[aswamy]

Is your feature request related to a problem? Please describe.

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Describe the solution you'd like

Most context.* params are static. However, metaobjects are dynamically defined on the shop-level. When you want to auto-complete that param, you must first fetch metaobjects from the shop.

{% content_for "block", id: 5, context.metaobject.foo█ %}  -> `foobar`

NOTE: This will require metaobject completion before starting this ticket.

Checklist

• [x] I have checked and made sure that the proposal adheres to this plugin's principles