Make Inspector implement DataSource

[johansolbakken]

• Working towards rendering JSON using the data disclosure API.
• Many of the components that are to be rendered expose their state using the inspector interface.
• This PR makes Inspector implement DataSource.
• The inspector interface has a default implementation for emit that prefers UTF-16 for strings.
• Subclasses can override emit to provide UTF-8 and UTF-16 directly for better performance.
• Since the inspector is a part of data access, it makes sense for it to implement a data source.

@andreer please review
@havardpe please review