feat(react-scripts): allow PUBLIC_URL in develoment mode

Created by: iamandrewluca

Allow PUBLIC_URL in development mode

• Feature (react-dev-utils/getPublicUrlOrPath)
• Tests
• Docs
• Types DefinitelyTyped/DefinitelyTyped/pull/40982

Public API

• In development mode browser is opened at desired pathname
• Redirect to desired pathname if does not start with it (react-dev-utils/redirectServedPathMiddleware)
• Assets will be served at desired pathname (webpack/webpack-dev-server/pull/2150)
• If desired pathname is a relative path, app will be served at /

Private API

• Combined paths.publicUrl and paths.servedPath into paths.publicUrlOrPath
• Extracted all logic into react-dev-utils/getPublicUrlOrPath (no side effects)
• Moved evalSourceMapMiddleware and errorOverlayMiddleware first in the middleware chain, redirect does not affect them.
• Moved proxy middleware after redirect (this is the case what most want, proxy should respect PUBLIC_URL
• Adapted noopServiceWorkerMiddleware to serve from servedPath
• Updated webpack-dev-server@3.9.0 to webpack-dev-server@3.10.0

Blocked by webpack/webpack-dev-server/pull/2150 Blocked by webpack/webpack-dev-server/pull/2374 Blocked by https://github.com/webpack/webpack-dev-server new patch release

Closes #6280
Closes #6135 (closed)
Closes #4158