Make esbuild optional

[joshkel]

Why am I submitting this PR

esbuild is a large dependency, and pinning to a specific version makes it less likely that it can be shared across other dependencies. To make i18next-parser lighter:

• Dynamically import esbuild if needed. Change esbuild to an optional peer dependency.
• Update the version range.
• Try loading .ts files using Node.js support for stripping TypeScript types (enabled by default in current Node.js versions), to potentially remove having to import ESBuild at all.
• Allow loading .mts as well as .ts.

This is a potentially breaking change: if a someone uses a .ts i18next-parser configuration, doesn't have type stripping enabled (or has a configuration file that's incompatible with Node.js's type stripping), and doesn't otherwise have esbuild installed, then they'll have to install it.

Does it fix an existing ticket?

No

Checklist

• only relevant code is changed (make a diff before you submit the PR)
• do no modify the version in package.json or CHANGELOG.md
• tests are included and pass: yarn test (see details here) (Preexisting .ts functionality didn't have tests - if you want me to see about adding these, let me know.)
• documentation is changed or added (I don't believe any updates to the documentation are needed)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.57%. Comparing base (398b9ce) to head (c725eda).
⚠️ Report is 44 commits behind head on master.

Files with missing lines	Patch %	Lines
src/helpers.js	0.00%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1150      +/-   ##
==========================================
- Coverage   95.35%   94.57%   -0.79%     
==========================================
  Files          10       10              
  Lines        1918     1990      +72     
==========================================
+ Hits         1829     1882      +53     
- Misses         89      108      +19     

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