Added a transpile-only ESM loader (#1101)

[concision]

This resolves the feature request #1101: A new ESM loader equivalent of 'ts-node/register/transpile-only'

[codecov]

Codecov Report

Merging #1102 into master will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@## master #1102 +/- ##
=======================================
Coverage 75.49% 75.49% =======================================
Files 7 7 Lines 657 657 Branches 148 148 =======================================
Hits 496 496 Misses 107 107 Partials 54 54 

Flag	Coverage Δ
#node_10	72.15% <ø> (ø)
#node_12_15	72.53% <ø> (ø)
#node_12_16	72.53% <ø> (ø)
#node_13	75.19% <ø> (ø)
#node_14	75.19% <ø> (ø)
#typescript_2_7	75.03% <ø> (ø)
#typescript_latest	74.27% <ø> (ø)
#typescript_next	74.12% <ø> (ø)
#ubuntu	75.19% <ø> (ø)
#windows	75.34% <ø> (ø)

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[coveralls]

Coverage increased (+1.0%) to 83.175% when pulling 525b730 on concision:ab/1101 into ce7c323 on TypeStrong:master.

[cspotcode]

Looks good but it'll need tests before being merged, and our package.json will need to be updated.

You can probably copy-paste an existing ESM test, but add a deliberate type error to make sure it gets ignored.

We also have tests that each entrypoint can be resolved, which will validate the changes to package.json.

[cspotcode]

Needs package.json updates and tests; otherwise looks good.

[concision]

I have added esm/transpile-only.mjs to the package.json exports and corresponding resolution tests.

I also added two tests to verify the loader should behave as expected:

• verify that the transpile-only ESM loader skips type checks in the presence of type errors
• verify that the transpile-only ESM loader throws a type error in the presence of type errors

Are there any other needed changes I need to make?

[cspotcode]

Looks great; just a couple questions.

[cspotcode]

@concision looks great, thanks. It's merged. I need a review of #970 before making our next release, but hopefully we can get that done this weekend. It'll be 9.0.0