Don't start the extension host in debug mode by default

[roblourens]

We start the extension host in debug mode at launch to support easy profiling and debugging it. This was reported as a potential vulnerability . Thanks to Francesco Soncina (MSRC 53814) and Tavis Ormandy (MSRC 54281).

This issue is already fixed in Insiders, but it depends on Electron 6 so we are preparing a simpler fix for stable.

The fix prevents the extension host from starting in debug mode by default. It will only start in debug mode if explicitly opted-in to with the --inspect-extensions flag. This flag is set for extension host debugging, auto profiling, and profiling/debugging through the "Show Running Extensions" page. EH debugging will work as normal, and the others will prompt the user to restart VS Code, and the EH will be started in debug mode.

[roblourens]

Fixed in 7f87a64