This allows users to build parsers without having to run `test` or
`parse` to invoke the compilation process, and allows them to output the
object file to wherever they like. The `build-wasm` command was merged
into this by just specifying the `--wasm` flag.
Previously, `tree-sitter build-wasm` had the ability to build WASM
by using docker to pull in an image with a complete emscripten toolchain.
This commit adds the ability to use podman to do the same thing.
Using podman requires two notable changes:
1. Using the fully-qualified image name. Docker defaults to prepending
`docker.io` to the image name, but podman does not.
2. Podman will mount the `/src/` volume as belonging to root unless
`--userns=keep-id` is passed. I think podman's different
volume-ownership is related to podman's daemonless execution and
`--uidmap` functionality, but I'm not 100% sure.
To test, I ran
```sh
script/fetch-fixtures
script/generate-fixtures
script/generate-fixtures-wasm # <- the important one!
```
which worked as well as the docker version.
