Convert field_ui_base_route entity property to #[FieldUiBaseRoute] attribute

Problem/Motivation

In #3443882: Allow attribute-based plugins to discover supplemental attributes to set additional properties we decoupled plugin definition properties by allowing optional attributes to exist alongside plugin attributes, which only have meaning once the module that owns the attribute is installed.

We initially tried to convert the field_ui_base_route entity property to an attribute, but the property is used outside of Field UI module so we might have to handle this in a backward compatible way with deprecations.

Steps to reproduce

Proposed resolution

Add the #[FieldUiBaseRoute] attribute.
Deprecate the field_ui_base_route property.

Remaining tasks

Figure out how to deprecate entity properties.

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet