Fix `apheleia-npx` in Yarn PnP projects

[zeorin]

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• apheleia-npx would use an incorrect path for the Yarn PnP ESM loader.
• apheleia-npx did not correctly guard against word splitting.
• apheleia-npx was sometimes not able to find formatters in a Yarn PnP project if there was also a node_modules folder at the root of the project. Unfortunately, many tools (including Prettier) will create a cache folder in node_modules even in Yarn PnP projects. The presence of any node_modules folders are irrelevant when a .pnp.cjs file is present.

[zeorin]

cc @edslocomb & @raxod502, as you were involved in https://github.com/radian-software/apheleia/pull/200.

[raxod502]

LGTM generally. Looks like upstream changes broke the tests. I'll fix, and also make sure we have test coverage that actually validates this change.

[raxod502]

Apologies to @zeorin for taking so long to look at this, notifications got lost in the shuffle

Also my fault because I was in the middle of working on this and it was still in progress but I have been busy with other things in my life and not attending to any of my GitHub notifications for a while, there are several dozen threads that have been waiting. This is still very much on my list if Ed doesn't beat me to it.

[raxod502]

Heyo, it turns out that I had got this pretty close to working already! The latest few changes seem to make things fully successful and now we have a proper test framework that supports ensuring that features like this will not break in the future.