Strict Mode Interpreter

[Lan2u]

ECMASCript feature
Strict mode support for the interpreter as per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode.

Example code

'use strict';
(14).sailing = 'home';

This code should throw a type error but currently returns 'home'.

The parser/lexer side of this was previously implemented as #717.

[raskad]

With #1550 we have strict flags available during the execution. I think we can close this and track individual implementations of strict handling in separate issues.