Upgrades prettier to 1.15.3
Runs `yarn prettier-save-all` against the codebase
Most changes are due to https://github.com/prettier/prettier/pull/5519

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/54807

This adds toggle buttons to switch between file & tree list.
For file list, it renders the truncated paths with the ellipsis
at the start of the path.

When focusing the input, it hides the toggle buttons.
On blur, the buttons get shown again.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/51859

This file tree displays all the diff files in a tree like format
Each file is taken and converted into a tree with folders
Each folder can be toggled open & closed
Clicking a file will scroll to the diff file & highlight with a glow affect

Searching the tree list will search only files & return a list of the
files without any folders

Each file row contains an icon to show changed, new file or deleted
Each row will also contain the added & removed lines count

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14249

The eslint-plugin-vue upgrade had some breaking changes to
vue/attribute-order which needed to be resolved in order to avoid
disabling the rule entirely

This makes the file row component re-usable ouside of the Web IDE

Pre-request for https://gitlab.com/gitlab-org/gitlab-ce/issues/14249