Detect Alpine Linux and download appropriate dart-sass release

[jgarber623]

From version 1.71.1 (released 20 Feb 2024), Dart Sass publishes a -musl variant suitable for use on Alpine Linux. We should update dart_sass to detect Alpine Linux and download and install the appropriate variant.

Doing so would (I believe) allow us to remove much of the related documentation from the FAQ section of the README. 🥳

In order to support this change (which may be a major version bump), the library would need to:

1. detect Alpine Linux (or more generally, "musl"),
2. update (or change) the Linux version detection code to >= 1.71.1, and
3. remove or update the relevant portions of the README