src/vs/platform/contextkey/common/contextkey.ts/ContextKeyDefinedExpr/substituteConstants
class ContextKeyDefinedExpr:	public substituteConstants(): ContextKeyExpression | undefined {
		const constantValue = CONSTANT_VALUES.get(this.key);
		if (typeof constantValue === 'boolean') {
			return constantValue ? ContextKeyTrueExpr.INSTANCE : ContextKeyFalseExpr.INSTANCE;
		}
		return this;
	}