Sidebar navigation missing when viewing docs using file:// protocol

[floscher]

Describe the bug
When I run ./gradlew dokkaHtmlMultimodule on my machine and then try to view the generated docs in the browser, the navigation is not displaying.

I'm trying to figure out how to setup a project with the new Dokka. For a long time I thought I had something misconfigured, because I could not see any navigation (see screenshots). Finally I discovered that the Console in the DevTools displays an error that a CORS request is blocked, because a protocol other than http:// or https:// is used.
See https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS/Errors/CORSRequestNotHttp for details on the error message.

This means that the navigation only displays if the docs are served over HTTP(S), but not if you want to view them in your local filesystem using the file:// protocol

Expected behaviour
There should be a navigation sidebar

Actual behaviour
The sidebar is completely empty. Error message in DevTools console.

Screenshots

To Reproduce
Open documentation generated by Dokka in the browser using the file:// protocol

Installation

• Operating system: Linux
• Build tool: Gradle v6.5.1
• Dokka version: 1.4.0-rc
• Browser: Firefox 79.0, Chromium 84.0

[MarcinAman]

closing in favour of: #1795 as it is planned for 1.5