Copy file templates to Classy

(First, verify that the preprocess changes have been made. #2322163: [meta] Consensus Banana Phase 1, move CSS classes from preprocess to twig templates.)

1. Copy the Twig templates from the core module's templates directory to Classy's templates directory. Include all templates, even ones without classes.
2. Remove all classes from the core module's template. Remove all classes added with addClass and ones that are hard-coded in the template.

• If there are classes that are required for basic functionality, discuss whether they should be kept.
• If there is CSS from the module, or anywhere else, referring to the class, discuss removing it or moving it to Bartik&Seven. Do not move the CSS to Classy.

Twig Templates to Copy

core/modules/file/templates/file-link.html.twig
core/modules/file/templates/file-managed-file.html.twig
core/modules/file/templates/file-upload-help.html.twig
core/modules/file/templates/file-widget-multiple.html.twig
core/modules/file/templates/file-widget.html.twig