Fix circularity in dependency tree + add CI check for circularity

[Gerrit0]

According to madge, TypeDoc currently has 7 circular dependencies.

1) lib/converter/context.js > lib/converter/converter.js
2) lib/models/types/index.js > lib/models/types/array.js
3) lib/models/types/index.js > lib/models/types/indexed-access.js
4) lib/converter/index.js > lib/converter/nodes/index.js > lib/converter/nodes/enum.js
5) lib/converter/index.js > lib/converter/nodes/index.js > lib/converter/nodes/variable.js
6) lib/output/renderer.js > lib/output/plugins/index.js > lib/output/plugins/AssetsPlugin.js
7) lib/output/renderer.js > lib/output/themes/DefaultTheme.js > lib/output/theme.js > lib/output/utils/resources.js

#1172 was caused by adding another circular dependency that (unlike the existing 7) was not deferable, and thus caused an application crash when using the CLI. (I still don't really understand why it didn't crash the tests too)

This could have been prevented by a CI check that runs a check for circular dependencies and fails the build if any are detected.

• Fix existing circular dependencies in TypeDoc
• Add a check to CI so that introducing a circular dependency fails the build

[Gerrit0]

While doing this, it would be great to simplify the existing dependency tree. This is crazy large, it shouldn't need to be this big... seriously, it reminds me of the time I generated a dependency tree of literally everything installed on a linux box.

[Gerrit0]

TypeScript 3.8's type only imports / exports should also help with this - https://devblogs.microsoft.com/typescript/announcing-typescript-3-8-beta/#type-only-imports-exports