feat: splitChunks support usedExports

[JSerFeng]

Summary

Docs: WIP

We have runtime optimization for used exports, for example when we have two entries named foo and bar, and a shared module shared which exports 2 values foo and bar.

foo imports foo from shared

bar imports bar from shared

with default behavior, there will be 2 shared modules in the final output, one contains only foo export for foo entry, and one contains only bar export for bar entry.

This is great. But when it comes to splitChunks, there will be problem.

if we have a cacheGroup that can select shared, then the shared module maybe extracted into a separate chunk, thus the runtime optimization is gone.

Now if you enable splitChunks.usedExports, when shared module is selected by a cacheGroup, the cacheGroup will calculate all possible combinations of how exports are used in different runtime.

shared with foo exported belongs to foo chunk, and with bar exported belongs to bar chunk, and if you didn't set cacheGroups.{cacheGroup}.name, then shared modules will still exist for both runtime.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[JSerFeng]

!bench

[rspack-bot]

📝 Benchmark detail: Open

Name	Base (2024-08-08 2bd905d)	Current	Change
10000_development-mode + exec	2.32 s ± 27 ms	2.32 s ± 36 ms	+0.13 %
10000_development-mode_hmr + exec	701 ms ± 7.3 ms	703 ms ± 7.5 ms	+0.31 %
10000_production-mode + exec	2.85 s ± 23 ms	2.89 s ± 41 ms	+1.54 %
arco-pro_development-mode + exec	1.89 s ± 75 ms	1.91 s ± 78 ms	+0.95 %
arco-pro_development-mode_hmr + exec	434 ms ± 2.4 ms	434 ms ± 2.3 ms	0.00 %
arco-pro_production-mode + exec	3.52 s ± 286 ms	3.41 s ± 92 ms	-3.19 %
arco-pro_production-mode_generate-package-json-webpack-plugin + exec	3.54 s ± 235 ms	3.6 s ± 169 ms	+1.53 %
threejs_development-mode_10x + exec	1.72 s ± 15 ms	1.71 s ± 19 ms	-0.15 %
threejs_development-mode_10x_hmr + exec	826 ms ± 9.5 ms	832 ms ± 14 ms	+0.74 %
threejs_production-mode_10x + exec	5.53 s ± 29 ms	5.52 s ± 33 ms	-0.25 %