Make the demo compile with NDK

[floppyhammer]

Solving #472. Upgrade usvg to 0.20.0, which removes harfbuzz_rs dependency.

[floppyhammer]

The demo shows some artifacts on Android, which doesn't occur in the last release. I'll open another PR to handle that.

[jdm]

@bors-servo r+
Thanks!

[bors-servo]

📌 Commit 9c1f48a has been approved by jdm

[bors-servo]

⌛ Testing commit 9c1f48a with merge db0dfee...

[bors-servo]

💔 Test failed - checks-github

[jdm]

error[E0599]: no function or associated item named `from_file` found for struct `Tree` in the current scope
  --> utils/svg-to-skia/src/main.rs:16:22
   |
16 |     let tree = Tree::from_file(&input_path, &Options::default()).unwrap();
   |                      ^^^^^^^^^ function or associated item not found in `Tree`

[floppyhammer]

@jdm Should probably merge #493 first.