Add xtask arguments and refactor code

[Caellian]

ArgumentList is now used for passing a collection of arguments around. It's better than [AsRef<OsStr>] because it can accept a lot of different argument specifications:

• All AsRef<OsStr> types directly, without slices,
• [AsRef<OsStr>] same as before,
• Vec<OsStr>,
• Tuples of Into<ArgumentList> (all of the above and self), which get chained,
• Unit, i.e. empty tuples.

Basically, this makes it very easy to call commands - instead of having to convert all types into the same type and pack them into a slice, one can simply list all parameters in a tuple and it will be converted into a slice using the shortest conversion route.

So calls that previously looked like:

cmd(&command,
&[
    file.as_os_str(),
    OsStr::new("-O3"),
    OsStr::new("--enable-bulk-memory"),
    OsStr::new("-o"),
    output.as_os_str(),
])

, now look like:

cmd(&command,
(
    file,
    "-O3",
    "--enable-bulk-memory",
    "-o",
    output,
))

That's a small example, there's cases where this visual noise has been significantly reduced as well as several intermediate variables removed.

Other changes:

• Restructured xtask code into modules.
• Moved distributables from typst-package into dist folder.
  • typst-package now only contains actual package sources (and manual).
• Made manual build reproducible by specifying last change time as build time instead of using current system time.
• Simplified code that handles configuration by using a trait that coalesces input types instead of previous macros.
• Improved cross-platform support for strings in Configure.