Convert FieldApiDataTest into a kernel test

Problem/Motivation

FieldApiDataTest is making no HTTP requests but is a functional test.

Proposed resolution

1. Convert FieldApiDataTest into a Kernel test.
2. Polish to make it more readable.
3. Cleanup ::setUp() and move object creation only in tests that actually use them so that they are not unnecessary created every time.

Remaining tasks

None.

User interface changes

None.

API changes

None.

Data model changes

None.

Release notes snippet

N/A