Move file export

[renefloor]

:sparkles: What kind of change does this PR introduce? (Bug fix, feature, docs update...)

Bug fix similar to #321

:arrow_heading_down: What is the current behavior?

File is always imported with the library conflicting with dart:io

:new: What is the new behavior (if this is a feature change)?

Give the user of the library a different way to import the file class

:boom: Does this PR introduce a breaking change?

It reverts a breaking change

:bug: Recommendations for testing

:memo: Links to relevant issues/docs

Fixes #320

:thinking: Checklist before submitting

• [X] All projects build
• [X] Follows style guide lines (code style guide)
• [X] Relevant documentation was updated
• [X] Rebased onto current develop

[renefloor]

@sidrao2006, @akadatsky and @aideric. What do you think of this solution? This way the default import

import 'package:flutter_cache_manager/flutter_cache_manager.dart';

won't conflict with dart:io, but you'll still have the option to add an import with

import 'package:flutter_cache_manager/file.dart';

[sidrao2006]

Yep, this is better than having to add file as a direct dependency

[codecov[bot]]

Codecov Report

Merging #324 (11c6dc5) into develop (b1e9807) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #324   +/-   ##
========================================
  Coverage    74.85%   74.85%           
========================================
  Files           21       21           
  Lines          672      672           
========================================
  Hits           503      503           
  Misses         169      169           

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