Key binding on view item command doesn't provide the view item

Issue Type: Bug

This is easily reproducible using the tree-view-sample repo.

1. Add a key binding for nodeDependencies.editEntry
2. Open the package explorer view and click on one of the nodes
3. 🐛 execute the key binding and notice the command fails (while if you click the pencil icon it will work fine)

When the command gets executed from the key binding it isn’t getting the proper context. This breaks most key bindings for commands on view items.

/cc @jrieken

VS Code version: Code 1.33.1 (51b0b28134d51361cf996d2f0a1c698247aeabd8, 2019-04-11T08:27:14.102Z) OS version: Windows_NT x64 10.0.18362

System Info

Item	Value
CPUs	Intel® Core™ i7-6700K CPU @ 4.00GHz (8 x 4008)
GPU Status	2d_canvas: enabled checker_imaging: disabled_off flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: disabled_software rasterization: enabled surface_synchronization: enabled_on video_decode: enabled webgl: enabled webgl2: enabled
Memory (System)	31.93GB (15.81GB free)
Process Argv
Screen Reader	no
VM	0%

[joaomoreno]

Yes. We could potentially have a sort of IContextKeysProvider feature at the Workbench(List|Tree) level which would do this for you. Something like:

interface IContextKeysProvider<T> {
    getContextKeys(element: T) { key: string, value: string }[];
}

Or so.

[joaomoreno]

When the command gets executed from the key binding it isn’t getting the proper context.

What the the expected context? That somehow viewItem is the selected/focused tree item? If so, the custom tree view needs to create a scoped context key service in which it sets the viewItem context as the tree selection/focus changes. That way, the context will be set when the user invokes the keybinding and has DOM focus inside the custom tree view DOM element.