MacOS keyboard shortcuts don't (all) apply when File Open/Save dialog is presented

[technicalflaw]

• VSCode Version: Code 1.15.0 (8b95971, 2017-08-09T20:06:21.685Z)
• OS Version: Darwin x64 16.7.0
• Extensions:

Extension	Author (truncated)	Version
vscode-markdownlint	Dav	0.10.0
beautify	Hoo	1.1.1
vscode-eslint	dba	1.2.11
vscode-dash	dee	1.7.0
python	don	0.7.0
vscode-html-css	ecm	0.1.7
vscode-npm-dependency	how	1.1.4
svg	joc	0.0.9
docthis	joe	0.4.7
Go	luk	0.6.63
HTMLHint	mka	0.3.3
debugger-for-chrome	msj	3.1.7
stylelint	shi	0.28.0

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Steps to Reproduce:

1. Do something to cause the standard Mac 'Save As' sheet to open (e.g. create a new file and go to File->Save As
2. Use a standard shortcut combination (standard in the context of the OS, not VSCode), such as cmd-A to select all text in the 'Save As:' field, or Ctrl-Tab to switch focus to the file list.
3. These expected actions don't occur for these specific examples, and presumably others as well, because they are still handled by the app (hence the flash of the relevant menu item when the aforementioned examples are used.

Reproduces without extensions: Yes

[bpasero]

This issue has already been reported. Please use the search function next time before reporting an issue and/or this time if you are curious about the progress of the issue.

[brandonbloom]

@bpasero When closing duplicates, please link to the original. I was able to find this issue, but it took several tries to find the other one that is already closed: #797

I can not find an open issue. I'm experiencing this issue. Is this a regression?