[Feature Request][dart] support Dart

[jeffhx]

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This API is available now (and has been improved a bit in the current Insiders). You'd define some json, and then an associated TreeDataProvider:

"views": {
	"explorer": [
		{
			"id": "dartFileOutline",
			"name": "File Outline",
			"when": "resourceLangId == 'dart'"
		}
	]
},

It would be great to see vscode-code-outline support Dart.

[patrys]

This extension will support any language as long as there is a language-specific extension that implements the SymbolProvider API for VS Code. Code Outline does not have any language-specific code.