Adds ts-node/register/transpile-only as require option

[godu]

istanbuljs/nyc#1124 (comment)

When we enable nyc.all option, nyc need to transpile source in the same way as the test runner (mocha or ava in my case).

If we add --require ts-node/register/transpile-only as default configuration for typescript, --all will work out of the box.

[coreyfarrell]

I don't think this can be in the preset as some people might want to use ts-node/register (not transpile-only).

Maybe it would be better to just update the documentation to suggest the require in nyc config instead of mocha config? @JaKXz this more your area so I'll defer to your judgement for how to handle this.

[godu]

Do someone realy want to use ts-node/register instead of ts-node/register/transpile-only ?
We only only the transpiler part of typescript here. It will be more efficient I think.

What uses --require apart from to transpile source when --all is enabled ?

[coreyfarrell]

What uses --require apart from to transpile source when --all is enabled ?

This also causes sources to be processed when actually running the tests.

[JaKXz]

@godu the reason I'm against this is that the default mocha setup does not need nyc to require ts-node at all - unless this has changed recently, I would rather leave it so that people don't have to do

"extends": "@istanbuljs/nyc-config-typescript",
"require": []

[godu]

@JaKXz seems legit

I rework my PR to add some documentation about require. Tell me if you have any others requirements.

[JaKXz]

@godu I appreciate that, but I don't think this adds any value to the package README, since it already mentions an .nycrc file.