[12.x] Add context remember functions

[btaskew]

Inspired by the Cache::remember function, adding Context::remember and Context::rememberHidden functions.

Context::remember will add the result of the provided closure function to the context if not already present, and always return the result

// Before
if (Context::has('user-permissions')) {
    $permissions = Context::get('user-permissions');
} else {
    $permissions = auth()->user()->permissions;
    Context::set('user-permissions', $permissions);
}

// After
$permissions = Context::remember('user-permissions', fn() => auth()->user()->permissions)

Useful when storing complicated values, or the result of DB queries, that you may need to access again elsewhere

[devajmeireles]

I think this is useful and I don't know how the Context was released without this 😅 But the implementation should be improved. I mean, for example, instead of accepting only a closure as the value, we could accept a mixed value to be interpreted by the value helper function.

[btaskew]

Have updated to use value helper as suggested