fix(state): unsub to subscribed context on disconnect

[rax-it]

No description provided.

[rax-it]

It seems we can't do

hideChild = false; instead of showChild = !false;

because then the template will look like:

<template lwc:if={!hideChild}>

which is also not allowed in lwc because of

[CompilerError: Invalid expression {!showChild} - LWC1060: Template expression doesn't allow UnaryExpression] {
  level: 1,
  code: 1060,
  filename: 'contextParent.html',
  location: { line: 3, column: 13, start: 41, length: 19 }
}

[rax-it]

Required to use non-registered symbols as WeakMap keys, more details here

[rax-it]

reverted to es2021, as per our discussion