"workbench.experimental.editorAssociations" should let you set association to "default" to use VS Code's normal viewer

[mjbvz]

Issue Type: Bug

The workbench.experimental.editorAssociations setting should support using the value "default" to force a given file to be opened using VS Code's standard editor

VS Code version: Code - Insiders 1.39.0-insider (211fa02, 2019-09-11T06:12:03.831Z)
OS version: Darwin x64 18.7.0

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-4770HQ CPU @ 2.20GHz (8 x 2200)
GPU Status	2d_canvas: enabled flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: enabled oop_rasterization: disabled_off protected_video_decode: unavailable_off rasterization: enabled skia_deferred_display_list: disabled_off skia_renderer: disabled_off surface_synchronization: enabled_on video_decode: enabled viz_display_compositor: disabled_off webgl: enabled webgl2: enabled
Load (avg)	3, 2, 2
Memory (System)	16.00GB (0.90GB free)
Process Argv	-psn_0_3461965
Screen Reader	no
VM	0%

[mjbvz]

Verification:

1. In a workspace with a png file

2. First verify that opening the png file shows the normal image view.

3. Now set:

   "workbench.experimental.editorAssociations": [
       {
           "filenamePattern": "*.png",
           "viewType": "default",
       }
   ],
   

   The point of this setting is to make VS Code use its default editor for png files (i.e. the text/binary editor)

4. Open the png file again and verify that it is now using the standard binary editor (not the image preview)