Ensure X11 connections are closed

[wez]

Checklist

• Run cargo clippy.
• Run cargo clippy --target wasm32-unknown-unknown if applicable.
• Add change to CHANGELOG.md. See simple instructions inside file.

Connections
#3813

Description
Introduces a DisplayOwner struct to own both the library and associated display pointer; their lifetimes are combined in that struct.

The display pointer is encapsulated in a DisplayRef.

When DisplayOwner is dropped, it ensures that the DisplayRef is correctly closed prior to unloading the library.

This PR looks bigger than it really is because of rustfmt'd whitespace changes in the main part of the code.

Testing
As explained in #3813, the hello example is modified to create multiple Instances, and then pause before shutting down the program.

Then in another window: lsof -p $(pgrep hello) | grep STREAM | wc -l is used to count the number of open descriptors. Prior to this change the count correlated with the number of Instances created by the program. With this change there are 0.

Note: the state of trunk at the moment has a unexpectedly passing test; that is not due to this change:

--- STDERR:              wgpu-test::wgpu-tests shader::struct_layout::uniform_input ---
thread 'shader::struct_layout::uniform_input' panicked at 'UNEXPECTED TEST PASS: FailureReasons(BACKEND)', /home/wez/wez-personal/github/wgpu/tests/src/lib.rs:330:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace