Enumerations-API refinement

[johnkerl]

As of 1.5.0rc0, SOMADataFrame.create takes three new arguments, and should not.

• create needs to take no new arguments
  • Those three values must be inferred from the passed-in Arrow schema
• write will present new levels

Core support:

• Permit zero levels at create (currently >= 1 is required)
• Offer a streamlined extend_enumeration API

Out of scope and separately tracked: bit-width mutation for when the level-count passes the 8-bit or 16-bit boundary: #1745

This is multi-developer work involving @davisp @nguyenv @eddelbuettel @johnkerl ; mainly this issue mirrors [sc-34800].

Additional reminder: R/Python interop cases within apis/system/tests.

[johnkerl]

[sc-34800]

[johnkerl]

Sub-issue: #1867