[base] A fix + example schema demonstrating named reference types

[bjoerge]

This fixes an issue with previews that broke when you had named reference types in arrays / block editor, and adds a few examples of named reference types to the example-studio schema, see:

sanity/packages/example-studio/schemas/referenceTest.js

Lines 8 to 24 in b26faff

	{
	name: 'arrayOfNamedReferences',
	type: 'array',
	of: [
	{
	type: 'reference',
	name: 'authorReference',
	to: [{type: 'author', title: 'Reference to author'}]
	},
	{
	type: 'reference',
	name: 'blogpostReference',
	to: [{type: 'blogpost', title: 'Reference to blog post'}]
	}
	]
	}
	]

and

sanity/packages/example-studio/schemas/blocks.js

Lines 17 to 27 in b26faff

	{
	type: 'reference', name: 'authorReference',
	to: {type: 'author'},
	title: 'Reference to author'
	},
	{
	type: 'reference',
	name: 'blogpostReference',
	to: {type: 'blogpost'},
	title: 'Reference to blogpost'
	},

(cc @skogsmaskin, @simen)

[rexxars]

Is the name stored in any way in the actual data? If so, on which property?

[bjoerge]

The name will be stored on _type, e.g.:

{_type: 'authorReference', _ref: 'henrik-ibsen'}

[rexxars]

LGTM.