Fix grant import

[gallois]

This fixes the issue described in https://github.com/petoju/terraform-provider-mysql/issues/112 where it's not possible to import some grants. In short, it:

• Adds type for parsing the grant resource from data, desiredProcedureGrant, separating it from desiredGrant, which now becomes desiredTableGrant. This is used when trying to find a conflict and can probably be made a bit more generic, but it's likely outside the scope of this change (see below)
• Refactors the old formatDatabaseName into produceGrantId which, as the name says, produced the grant id that is going to be used by the provider.
• Sets some additional required fields for importing the grants, the most important one being the id which was missing and causing the errors that were seen in the issue above.

It also fixes a typo in the docs that I introduced earlier.

There are a few things worth noting:

• Role grants are not covered. Unfortunately, I don't currently have a use case for that, so there's no good way of testing it properly.
• As mentioned before, there are parts of the code that could be refactored to be more generic. That being said, it would also require implementing the fixes for role grants to write it in such a way that it would be properly generic.

[gallois]

Got it. I'm afraid I'm a bit time-constrained right now to be able to implement additional changes, mostly because "it works on my machine"™

I'll close this PR for now and keep following https://github.com/petoju/terraform-provider-mysql/issues/112 to ensure I jump back to upstream when it's fixed.

Thanks a lot for the effort in maintaining it :)