Simplify TypeScript configuration

[lostfictions]

As I tried to figure out how to upgrade to React Hot Loader 4 today, I was a bit confused by the options for configuring it for use with TypeScript -- it seems less than ideal to chain loaders, and in particular requiring folks to change their tsconfig is pretty annoying. Either way, there's a performance hit.

I think the ideal, most non-disruptive solution for TypeScript users would be for RHL to eventually support a TypeScript custom transform plugin as discussed here -- but for now, since Babel can consume TypeScript syntax and transpile it, why not recommend using it alone as the simplest method? There's no requirement for users to change their tsconfig, rebuilds are lightning-fast, and you can still typecheck with fork-ts-checker-webpack-plugin (or manually invoking tsc --noEmit).

In this PR I've provisionally updated the README with more verbose (but hopefully simpler) instructions and changed the TypeScript example to reflect this configuration -- maybe folks can try it out and see what they think?

[codecov-io]

Codecov Report

Merging #996 into master will not change coverage.
The diff coverage is n/a.

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[theKashey]

I think - its time to create a separate TS documentation file, with more deeper explanations, as long - we have got tooooo many variants.

[micimize]

the preset here depends on @babel/plugin-transform-typescript, which among other things doesn't support namespaces. I think the syntax-typescript the previous babel-only setup used has the same problem (they don't say explicitly).

For some people the performance is worth the trade-off, but it should be noted. I personally wasn't able to get a functioning typescript-first config with my environment, I think because of allowSyntheticDefaultImports or some other setting.

[theKashey]

allowSyntheticDefaultImports does not change the way code got generated.
I thing we have to make a pause, and outline all possible way to handle TS, more examples to test, and all caveats found.

[theKashey]

merged as a part of another PR