suggestion: remove `_util/assert.ts`

Please read #2846 before reading this. I suggest moving std/testing/asserts.ts to either an std/testing/asserts or std/asserts folder with an assertion-per-file. The folder would look more like std/fs.

Indeed, there is a large number of assertions, meaning there will be a large number of files. However, I think this is worth it to gain leaner assertion-related dependencies.

The files will have to be moved out, and then std/testing/asserts.ts functions deprecated. It’d be a bit of work, but I’d be happy to do it.

[cjihrig]

I agree with @kt3k

[kt3k]

We create an internal version of each assertion that uses DenoStdInternalError and put it in _util/asserts.ts.

I don’t think it’s worth it because we probably only need assert for internal assertions (and the usages are not so much increasing). Maybe let’s add others when they are needed.

We create a tool that enforces use of _util/asserts.ts using deno_graph.

I think this would be useful.