Feature request: Optional configuration option to change "Create Playground" tmp directory

[nakato]

Version of VSCode: 1.20.0
Version of the extension: 0.42
OS: Arch Linux

Description: Optional configuration option to change "Create Playground" tmp directory

Output of the "Rust logging" channel:
N/A

Problem:
On many Linux installations, /tmp is a tmpfs, and some people will run their systems without swap, or may already be heavily in swap. Placing the playgrounds in /tmp in these situations may result in system instability, such as OOMKiller being called, or other issues that only occour during extreme memory pressure.

To solve this without having to mount a device backed /tmp or creating a large swap partition I would like to be able to configure the directory that the create playground command uses place the playgrounds into.