Avoid loss of all permissions/roles pivots on sync error

[erikn69]

Closes #2339

Describe the bug
When using the syncPermissions function from the HasPermissions trait, providing an accidental wrongly named permission will result in loss of all permissions. This is caused by the fact that syncPermissions eagerly removes all existing permissions.

Steps to reproduce the behavior:
Create a model that uses the HasPermissions trait
Assign some valid permissions to the model
Use the syncPermissions helper, with a combination of any number of valid permissions and at least one invalid permission
Result: all permissions will be lost on the user

Example Test
Here is a link to my Github repo containing a minimal Laravel application which shows my problem:
main...jnoordsij:spatie-laravel-permission:permission-sync-fail

[drbyte]

Note: in #2182 when this collectPermissions() method was created, it was created by @angeljqv as public, but probably should have been private.
It was released in v5.5.7.

Since it's a breaking change, albeit highly unlikely to affect anyone, we won't backport this to v5.

[angeljqv]

Ok, i did test it, it works correctly for me, seems the right way

[drbyte]

Thanks @erikn69 !