Snap: Register code as an editor in Debian with update-alternatives

Issue Type: Bug

This is a bug report regarding a feature that was implemented here: https://github.com/microsoft/vscode/issues/3541

1. Install Ubuntu 18.04 LTS
2. Open Snap Store aka "Ubuntu Software"
3. Search for VSCode
4. Click on VSCode
5. Click install
6. Wait for install to complete
7. Open terminal
8. run "update-alternatives --config editor"

Expected: VSCode appears as an option. See https://github.com/microsoft/vscode/issues/3541 Actual: VSCode does not appear as an option

VS Code version: Code 1.43.1 (fe22a9645b44368865c0ba92e2fb881ff1afce94, 2020-03-18T07:17:38.324Z) OS version: Linux x64 5.3.0-42-generic snap

Item	Value
CPUs	Intel(R) Core(TM) i7-4770 CPU @ 3.40GHz (8 x 3829)
GPU Status	2d_canvas: unavailable_softwareflash_3d: disabled_softwareflash_stage3d: disabled_softwareflash_stage3d_baseline: disabled_softwaregpu_compositing: disabled_softwaremultiple_raster_threads: enabled_onoop_rasterization: disabled_offprotected_video_decode: disabled_offrasterization: disabled_softwareskia_renderer: disabled_off_okvideo_decode: disabled_softwareviz_display_compositor: enabled_onviz_hit_test_surface_layer: disabled_off_okwebgl: unavailable_softwarewebgl2: unavailable_software
Load (avg)	1, 0, 0
Memory (System)	31.27GB (24.04GB free)
Process Argv	. --no-sandbox
Screen Reader	no
VM	0%