Change Start Debugging Extension Host on Running Extensions to not require a restart

Issue Type: Bug

Currently if you click on Start Debugging Extension Host from the Running Extensions tab it will ask you to restart. This IMO defeats the main purpose of this feature, as the only times I want to do this, is when I am seeing an extension issue that I can't easily reproduce and when to debug it when it is happening.

Related -- it would be great to not attempt to attach in the same vscode instance and instead open a new vscode window to attach from.

VS Code version: Code - Insiders 1.41.0-insider (599c076d91be1374cf51004cec610f3bcaf4c9cd, 2019-11-22T07:25:24.031Z) OS version: Windows_NT x64 10.0.19028

Item	Value
CPUs	Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz (8 x 4008)
GPU Status	2d_canvas: enabledflash_3d: enabledflash_stage3d: enabledflash_stage3d_baseline: enabledgpu_compositing: enabledmetal: disabled_offmultiple_raster_threads: enabled_onoop_rasterization: disabled_offprotected_video_decode: unavailable_offrasterization: enabledskia_renderer: disabled_offsurface_control: disabled_offsurface_synchronization: enabled_onvideo_decode: enabledviz_display_compositor: enabled_onviz_hit_test_surface_layer: disabled_offwebgl: enabledwebgl2: enabled
Load (avg)	undefined
Memory (System)	31.93GB (16.39GB free)
Process Argv
Screen Reader	no
VM	0%