chore(loader-utils): Preparing to migrate from FileProviders to ReadableFiles

[dariaterekhova-actionengine]

No description provided.

[ibgreen]

• Maybe outline your migration strategy in the PR comment?
• I mostly see a rename of an interface, would be good to understand how this will help the next step.

[dariaterekhova-actionengine]

The main purpose of this PR is to give an instrument to use ReadableFile in already existing code (newFileProvider implementation) and give an opportunity to use both old FileProviders and new ReadableFile implementations in the same time (FileProviderInterface), so we can migrate one old FileProvider at a time.

First I'm going to correct my implementation of slpk-via-rangerequests in another PR to use already existing HttpFile instead of new code