core: Fix stroke artifacts when using drawing API

Some recent changes with lyon's API could cause Ruffle to draw extra
strokes when it sees two Move commands in a row -- an extra zero-length
stroke would appear. Let's merge adjacent Move commands in the
tessellator to avoid this issue.

(TODO: Add an example to visual_tests).

web: Fix some context menu and warning message issues

chore: Revert "build(deps): bump quick-xml from 0.20.0 to 0.21.0"

This reverts commit 0c6c339.

ci: Fix publish AUR package job

ci: Publish nightly builds to the AUR

Add a new job to release_nightly.yml that updates the AUR package
https://aur.archlinux.org/packages/ruffle-nightly-bin/ on nightly
basis.

chore: Add wasm-bindgen-cli version to docs

build(deps): bump isahc from 1.0.3 to 1.1.0

Bumps [isahc](https://github.com/sagebind/isahc) from 1.0.3 to 1.1.0.
- [Release notes](https://github.com/sagebind/isahc/releases)
- [Commits](sagebind/isahc@1.0.3...1.1.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

core: Remove unneeded pub

chore: Add a few comments about unsafe usage

desktop: Fix sound envelopes to use proper positions

The points in an SWF sound envelope are always in 44.1KHz. The
desktop audio backend would end up using this points in the sound's
sample rate, often causing the envelope to be delayed.

Now the envelope is applied after resampling, and the positions
are scaled based on the output sample rate.