Improve behavior for PK values

[pavish]

Current behavior

• We allow editing/removing default values for all columns, including PK columns.
• We do not allow editing cells for PK columns.

Bugs due to the current behavior

• Users are able to remove a dynamic default value for PK columns. Once removed, adding any new row will fail.
• If no default value is present for a PK column, adding a new row will fail. Since we do not allow editing PK column cells, users will never be able to add a new row.

Expected behavior

• Users should not be able to remove/modify a dynamic default value of a PK column.
• Users should be able to edit a PK column cell in an un-saved row. They should not be allowed to do that for saved rows.
• Creating records via the Record Selector should also work smoothly when supplying PK values

[seancolsen]

Related: #1362, #1361

[pavish]

Blocked by #1672

[seancolsen]

I've done some research and exploration on this today and am closing this ticket with the following findings:

• Users should not be able to remove/modify a dynamic default value of a PK column.

  I've tested this and not been able to identify any UI that allows users to remove/modify dynamic default values in PK columns. I suspect the reporting of this issue came from before our Table Inspector changes.

• Users should be able to edit a PK column cell in an un-saved row. They should not be allowed to do that for saved rows. Creating records via the Record Selector should also work smoothly when supplying PK values

  I opened Should we allow users to specify PK values while adding records? If so, how? #2336 to discuss these points in more detail.