build tsdx with tsdx

[jaredpalmer]

We could compile tsdx with tsdx by first running it through tsc and then running it on itself.

We would need to change the repo's tsc outDir to something like tmp and then we would just run node ./tmp/index.js build ./tmp/index.js --tsconfig=tsconfig.compile.json. We would probs need to tweak tsconfig to make it work.

Kind of cool though. Probably useless.

[agilgur5]

Had been thinking of doing this too for dogfooding, but didn't see much of a point to it (would probably be slower to build too).

Could also use ts-node to simplify the above. Is there a reason ts-node isn't used internally? E.g. tests depend on the built dist/ files, which can be out-of-date (have tested the wrong version multiple times now); with ts-node could always use the current version. Can send a PR to improve the tests with it if there isn't anything against it

[agilgur5]

Not sure why neither of us wrote this, but actually the ideal way would be to use an old version of TSDX to build itself, as compilers or buildchains more broadly try to do.

build is the only piece that isn't dogfooded (well and create), so that would be one more type of self-integration test (could also do build with old version, re-build with currently built version).

I'm also looking to add project integration tests, e.g. building immer with a new version of TSDX and seeing if there are any breaking changes or, if it could run tests on dist code, seeing if those still pass