Numeric field prefix/suffix settings should be translatable

Problem/Motivation

On #2546212: Entity view/form mode formatter/widget settings have no translation UI and/or #2449597: Number formatters: Make it possible to configure format_plural on the formatter level I noticed that if you go to translate an Integer field, you do not get the option to translate the Prefix and Suffix fields. They definitely need to be translatable.

The problem is that they are config type "string" and it should be "label". This is in core/config/schema/core.data_types.schema.yml :

field.field_settings.integer:
  type: mapping
  label: 'Integer'
  mapping:
...
    prefix:
      type: string
      label: 'Prefix'
    suffix:
      type: string
      label: 'Suffix'

See also #2545730: Misuse of formatPlural() in Numeric field prefix/suffix

Proposed resolution

Change prefix/suffix to be type "label" instead. This should apply to all fields that have prefix/suffix.

Remaining tasks

Make a patch.

User interface changes

Prefix/suffix settings for numeric fields will be translatable.

API changes

None.

Data model changes

Not really. This is a compatible change -- the only difference between string and label is that label is marked as Translatable. So I don't think we need to migrate anything.