fix(core): export legacy root symbols from submodules instead of relative paths

[kuhe]

Issue

V2236964587

Description

This is a fix for older clients that import from @aws-sdk/core root level. The root should export submodules by name so they can re-resolve through the exports mappings rather than directly file-reference a submodule index.

Using relative paths prevents the conditional browser submodule exports from working.

Testing

CI

Checklist

• If the PR is a feature, add integration tests (*.integ.spec.ts) or E2E tests.
  • It's not a feature.
• My E2E tests are resilient to concurrent i/o.
  • I didn't write any E2E tests.
• I added access level annotations e.g. @public, @internal tags and enabled doc generation on the package. Remember that access level annotations go below the description, not above.
  • I didn't add any public functions.
• Streams - how do they work?? My WebStream readers/locks are properly lifecycled. Node.js stream backpressure is handled. Error handling.
  • No streams here.

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[kuhe]

rebase, restart CI after #8087