support collapsed::true

[CiceroIsBack]

Logseq currently collapses bullets when the collapsed::true property is added to them. VS Code already supports collapsing bullet points. It should not be hard for it to recognize the collapsed::true property, and automatically collapse bullets when that property is added.

This will make working with large markdown files much easier, and the collapsed state of blocks should sync seamlessly between Loam and Logseq.