Update to latest rust-layers

We now need to pass through the content age of the LayerBuffer when
creating it.
Mark all layers as having changed content during pinch zoom

This ensures that layers know that they need to re-issue buffer
requests immediately instead of waiting until another content change
happens.

Fixes #2988.
Make Attr::local_name an Atom.
Pass an Atom to before_remove_attr and after_set_attr.
Merge pull request #3097 from mrobinson/pinch-zoom-delay

Update rust layers and fix delay in pinch zoom
Ensure that block elements with replaced content don't get their block size overwritten.
Merge pull request #3105 from glennw/block-replaced-content

Ensure that block elements with replaced content don't get their block s...
Prevent margin collapse in the root flow

According to the CSS specification, section 8.3.1, margins of the root
element's box do not collapse. Ensure that root flow margins do not
collapse during the assign heights phase.
add rpath back for library build

this broke library usage completely when it was removed
Merge pull request #3106 from zmike/librarian

add rpath back for library build
Add doge Servo files for testing and demos
Merge pull request #3107 from mrobinson/root-margin-collapse

Prevent margin collapse in the root flow
Merge pull request #3109 from larsbergstrom/doge_files

Add doge Servo files for testing and demos
Replace hasInterfacePrototypeObject checks by isCallback checks in codegen.

Checking for callbacks directly makes it a lot clearer what's going on, and we
don't intend to take hasConcreteDescendant into consideration.

See also <https://bugzilla.mozilla.org/show_bug.cgi?id=1026720>.
Add a script to update the WebIDL parser.
Update WebIDL.py.
Stop artificially constraining the size of the GC heap.
Merge pull request #3113 from Ms2ger/update-webidl

Update WebIDL.py; r=Manishearth
Merge pull request #3112 from Ms2ger/hasInterfacePrototypeObject

Replace hasInterfacePrototypeObject checks by isCallback checks in codegen.
Merge pull request #3099 from Ms2ger/attr-local_name-atom

Make Attr::local_name an Atom; r=abinader