[meta] Deduplicate the set of available field types

Updated: Comment #25

Problem/Motivation

There's a duplicated set of field types in core (see Original report) but core's "initial field types does not have widgets and formatters.

Proposed resolution

Move email and number modules code into \Drupal\Core\Field\Plugin\Field.
Inherit them for text and number module at least

Remaining tasks

figure out the core's default formatters|widgets

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User interface changes

tbd

API changes

no

Original report by @yched

Most base fields still use the "initial" set of field types that were introduced with the initial Entity/FieldNG patch.
Those have no widgets/formatters, and many of them duplicate the "configurable field types"

- Needless duplicates means confusion & memory clutter for field type plugin definitions
email / configurable email
string / text
timestamps
booleans...
- we are starting to leverage widgets/formatters on base fields

Several issues are touching this area:
- #2010930: [META] Apply formatters and widgets to rendered entity base fields (all besides node.title) →
- sub-issues opened from #2112239: Convert base field and property definitions →
📌 Convert the description field of the 'aggregator_item' entity to a text field Active
#2149859: Convert the 'field_id' base field on comment entities to an entity reference field →
- some other issue I can't find about user signature
- ...

We probably should:
1) take a broader overview of our current list of "base only" field types, and decide what to do with each of them.
2) then open sub issues per entity type and change the field types of their base fields accordingly (will probably affect the base table schemas)