This is a step toward upgrading WebRender, which will be upgraded and
patched in the `third_party` directory. This change vendors the current
private branch of WebRender that we use and adds a `patches` directory
which tracks the changes on top of the upstream WebRender commit
described by third_party/webrender/patches/head.
Formats the following files:
* components/layout/display_list_builder.rs
* components/layout/webrender_helpers.rs
Remove outdated options from rustfmt.toml.
Configure rustfmt to place binary operators
at the end of line (to match ./mach test-tidy).
