[FEATURE]: Support exported types in the documentation coverage

[stijnbollen]

Overview of the feature

Documentation for declarations that start with export type should be added to the site's documentation coverage page.

Motivation for or Use Case

In my project I have several exported types that mutate both internal and external interfaces.
Because my colleagues should use these mutated interfaces instead of the ones they are based upon,
it is important that these types are properly documented.
The easiest way to validate the coverage of these exported types would be to have them listed in the same place as the classes, components and interfaces.

Examples of these exported types in my project are:

• Mutation of an external interface

/**
 * CSS Style Declaration object with optional properties (as it should be)
 */
export type CSSStyleObject = Partial<CSSStyleDeclaration>;

• Mutation of an internal interface

/**
 * Defines the font properties of a text, extends all properties with the currentable property flags
 */
export type ICurrentableFontDefinition = {
    [prop in keyof FontDefinition]: ICurrentableProperty<FontDefinition[prop]>;
};

Currently these types are added to the documentation, but not to the coverage page.

Related issues

Support exported type