chore(repo): use shell-emulator for better cross-platform compatibility

[danielbayley]

Rollup Plugin Name: *

This PR contains:

• [x] bugfix
• [ ] feature
• [x] refactor
• [ ] documentation
• [ ] other

Are tests included?

• [ ] yes (bugfixes and features will not be merged without tests)
• [x] no

Breaking Changes?

• [ ] yes (breaking changes will not be merged unless absolutely necessary)
• [x] no

If yes, then include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers:

Description

I started work on a separate PR, but quickly ran into errors with the prepare scripts apparently not being cross-platform (if command not found—I am on macOS). Since this is a pnpm monorepo, and the scripts are very simple, why not make use of the shell-emulator .npmrc config option (which uses yarnpkg-shell)? This also means the dependency on del-cli is no longer necessary.

[tada5hi]

failing wasm test should be unrelated to pr?! @shellscape

[danielbayley]

@shellscape Should be resolved now…