Multiple type support

[elbakerino]

Multiple types type: ["boolean", "null"] could be possible when widget is set for those.

Currently nothing will work with multiple types, but the actual implementation - if the ui is not selected by type - should be rather simple. The refactoring of existing usages may be the more problematic part.

The "used-for-validation" type can be get with the first plugin / after combination & referencing is executed. If not undefined and one of the specified types is valid, this type is used, otherwise "type-error" is set - but e.g. all further validators must do nothing then as no type can be used for "should the validator do something".

[elbakerino]

Implemented multiple type support, validators support JSON-Schema spec..

But rendering needs:

• custom widgets, handling "which type should be entered"
• using simple only one-scalar types and null for nullables, e.g.: "type": ["string", "null"]
  • as null is not counted as "input type" by schemaTypeToDistinct

Utility functions:

• import { schemaTypeToDistinct } from '@ui-schema/ui-schema/Utils/schemaTypeToDistinct';
• import { schemaTypeIs } from '@ui-schema/ui-schema/Utils/schemaTypeIs'
• import { schemaTypeIsAny } from '@ui-schema/ui-schema/Utils/schemaTypeIs'
• import { schemaTypeIsNumeric } from '@ui-schema/ui-schema/Utils/schemaTypeIs'