Don't install extensions through the code CLI

[dithpri]

The profile switcher invokes an external command to install an extension when switching the profile. binaryFullPath, which is set from getCodeBinary() runs into a similar issue as #46: trying to come up with the code executable's full path is buggy and unreliable.

(getCodeBinary() in my tests returns bin/code. But bin/code is not in $PATH, code is!)

Luckily, there's another way:

vscode.commands.executeCommand('workbench.extensions.installExtension', ext.publisherId);

cf. https://code.visualstudio.com/api/references/commands