Acorn 7.3.0 upgrade

[guybedford]

Acorn just released 7.3.0 with optional chaining support so this PR switches back from the fork we were using to provide this.

I did check that the final ESTree changes don't affect any of the internal code here and as far as I can tell there aren't any issues with this currently, but let me know if I've missed anything.

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

Description

[guybedford]

Because the build is performed based on the previous build I've left in the fork, perhaps a way to do this will be to remove the fork in a subsequent PR once this is merged?

[rollup-bot]

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install rollup/rollup#acorn-upgrade

or load it into the REPL:
https://rollupjs.org/repl/?circleci=11868

[codecov]

Codecov Report

Merging #3628 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3628   +/-   ##
=======================================
  Coverage   96.54%   96.54%           
=======================================
  Files         182      182           
  Lines        6243     6243           
  Branches     1832     1832           
=======================================
  Hits         6027     6027           
  Misses        107      107           
  Partials      109      109           

Impacted Files	Coverage Δ
src/Graph.ts	100.00% <ø> (ø)
src/Module.ts	98.90% <ø> (ø)
src/ModuleLoader.ts	100.00% <ø> (ø)
src/ast/nodes/NodeType.ts	100.00% <ø> (ø)
src/ast/nodes/index.ts	100.00% <ø> (ø)
src/utils/options/normalizeInputOptions.ts	98.05% <ø> (ø)
src/utils/pureComments.ts	100.00% <ø> (ø)

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[chicoxyzzy]

7.3.1 was released a bit later today

[guybedford]

I've also added a commit here to upgrade the plugins, as there was a fix in the private class elements package to work with optional chaining here - acornjs/acorn-private-class-elements@c9857bb.

I also removed the import meta plugin since that is in Acorn core since acornjs/acorn#943.

[lukastaegert]

Thanks!

Because the build is performed based on the previous build I've left in the fork

It is not, there was an alias in the Rollup config which replaced acorn by the fork. Which is why your branch was still running the fork. Fixing this revealed that we also needed the new ChainExpression to prevent Rollup from deoptimizing entirely, which I added.

I also removed the import meta plugin since that is in Acorn core

👍