fix(js): handle different exports field shapes

[jaysoo]

The exports field in package.json can have string values instead of objects, this will break if the user sets this for the . export.

Current Behavior

If user has a string in exports like exports: './index.js' then our JS build fails.

Expected Behavior

Custom exports with string should work, same with exports: { '.': './index.js' }.

Related Issue(s)

Fixes #

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✅ Successfully ran 12 targets

• nx affected --target=e2e --base=f26f2a1d3329ada175fe365eeb59e5d820feece7 --head=fe5634f33184e06a6b18ecfbfe397af4706989a1 --exclude=e2e-storybook,e2e-storybook-angular,e2e-react-native,e2e-detox,e2e-make-angular-cli-faster --parallel=1
• nx affected --target=test --base=f26f2a1d3329ada175fe365eeb59e5d820feece7 --head=fe5634f33184e06a6b18ecfbfe397af4706989a1 --parallel=1
• nx affected --target=build --base=f26f2a1d3329ada175fe365eeb59e5d820feece7 --head=fe5634f33184e06a6b18ecfbfe397af4706989a1 --parallel=3
• nx affected --target=lint --base=f26f2a1d3329ada175fe365eeb59e5d820feece7 --head=fe5634f33184e06a6b18ecfbfe397af4706989a1 --parallel=3
• nx-cloud record -- yarn depcheck
• nx-cloud record -- yarn nx workspace-lint
• nx-cloud record -- yarn check-lock-files
• nx-cloud record -- yarn check-commit
• nx-cloud record -- yarn nx format:check --base=f26f2a1d3329ada175fe365eeb59e5d820feece7 --head=fe5634f33184e06a6b18ecfbfe397af4706989a1
• nx-cloud record -- yarn check-imports
• nx-cloud record -- yarn documentation
• nx build typedoc-theme

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