feat(api): Extend getMetadata in Metadata API

[kajarosz]

This change extends getMetadata method in Metadata API in order to meet Metadata Sidebar Redesign needs as it will require less complex typing.

Currently MetadataSidebar fetches editors which are objects containing:

• template object - it holds data on which template was used to create metadata instance for current file and current user and most importantly it holds fields array. This array consists of field objects which hold details on field displayName, field type etc. but do not hold field value for current file and current user - this is job for instance object.
• instance object - as explained above is simple object with instance details like id and key-value pairs which reflect template fields keys.
  For now in order to get field details AND value for particular metadata instance, there's a lot of mapping needed which makes components implementation less straight forward. Additionally, more types are needed to handle that.

On the top of that, most of the above explanation is not valid in custom metadata case as it does not use templates. This makes whole logic even more complex.

We want to improve this in new Metadata Sidebar to simplify logic inside components and reduce number of types. In this change we are unifying data provided for metadata instances from template and custom metadata, so that components do not have to introduce any additional logic, checks etc. In redesigned Metadata Sidebar we'll introduce the same component for viewing both metadata instances from template and custom metadata instead of dedicated component for each type of instance.

[CLAassistant]

All committers have signed the CLA.

[wpiesiak]

what about:

Suggested change

	description: field.description,
	displayName: field.displayName,
	hidden: field.hidden,
	id: field.id,
	key: field.key,
	options: field.options,
	type: field.type,
	value: instance[field.key],
	...field,
	value: instance[field.key],

[kajarosz]

MetadataTemplateField has isHidden field which is not expected by MetadataTemplateInstanceField, but it's the only difference which does not collide that much. I implemented your suggestion.

[wpiesiak]

Suggested change

	displayName: template.displayName,
	hidden: template.hidden,
	id: template.id,
	metadataFields,
	scope: template.scope,
	templateKey: template.templateKey,
	...template,
	fields: metadataFields

[kajarosz]

I can't implement this as suggested because template: MetadataTemplate has isHidden field that we do not want to have in MetadataTemplateInstance. Moreover, template: MetadataTemplate already has fields defined which has incompatible type - it's type is Array<MetadataTemplateField> while MetadataTemplateInstance is expecting MetadataTemplateInstanceField[]. The difference in these two types is that the first one has isHidden and does not have value in comparison to second one.

All in all, I'd rather stay with my implementation.

[bfoxx1906]

lgtm