Make access control mode configurable

[turbolent]

Context

The type checker supports different "access check modes", i.e. the strictness of how access control modifiers are enforced. Currently the mode is hard-coded to be strict, i.e. all declarations must have an access modifier.

Make the setting configurable, so developers can choose what mode they prefer. This makes getting started with Cadence easier, as no effort has to be spent on providing correct access modifiers for declarations.

Definition of Done

• [ ] CLI: Add flag to let the developer choose access check mode
• [x] Language Server: Add a setting to let the developer choose access check mode
• [ ] Documentation

[10thfloor]

@turbolent Add documentation should be part of this issue, and others that propose to add new features.

[turbolent]

@10thfloor Good point, added