add ability to specify stdin file extension via --stdin=ext

[kzc]

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:

Addresses missing functionality mentioned in #3312.

Description

Presently rollup can only process esm via stdin. This PR adds the ability to specify the CLI stdin file extension via --stdin=ext allowing other inputs such as JSON:

echo '{"foo": 42, "bar": "ok"}' | rollup --stdin=json -p json

A synthetic file name "-.ext" is used internally to represent the stdin filename with an extension in order to work with existing plugins with suffix-based logic. Stdin based input can still be disabled with --no-stdin if required.

Unfortunately this new stdin extension feature will not work with plugins that interrogate the filesystem to read input files such as @rollup/plugin-typescript. For this scenario other plugins like @rollup/plugin-sucrase or rollup-plugin-esbuild could be used instead.

[codecov]

Codecov Report

Merging #3775 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3775   +/-   ##
=======================================
  Coverage   97.03%   97.03%           
=======================================
  Files         185      185           
  Lines        6465     6466    +1     
  Branches     1874     1875    +1     
=======================================
+ Hits         6273     6274    +1     
  Misses        101      101           
  Partials       91       91           

Impacted Files	Coverage Δ
cli/run/commandPlugins.ts	97.36% <100.00%> (ø)
cli/run/stdin.ts	100.00% <100.00%> (ø)

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[kzc]

The code coverage failure seems rather insignificant - a partial miss in one line.

@lukastaegert Feel free to take over this PR to change its testing and implementation as you see fit. It works fine my own use. I think others could benefit from this new functionality as well.

[kzc]

The code was simplified and coverage now passes.

[lukastaegert]

Thanks, looks good!