`eval` command: Escape HTML on the evaluated value.

[jvilk-stripe]

Many things that evaluates to a string do not work properly without this escape. For example:

• ""
• " "
• [].join (which produces " ")

Fixes a bug where the debug console in VS Code can hang the debugger when inserting one of those types of input.

I could not find tests for this routine. If I missed any, let me know!

[jvilk-stripe]

cc @hurricup