Add missing compiled browser entry points to package

[harmony7]

Which problem is this PR solving?

This PR fixes some missing files entries in package.json files. The missing entries would cause the module and esnext entry points to be excluded from the built NPM packages.

Short description of the changes

Some projects have "module" and "esnext" entries in their package.json, but the referenced files were not being included in their respective package due to them having been left out of the files section.

The issue applies to @opentelemetry/otlp-exporter-base and @opentelemetry/otlp-transformer and was causing problems under Webpack bundling for us.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Building the package locally using the corrected package.json generates a package that includes the missing files.
• Using this corrected package fixes the Webpack bundling problem I described above.

Checklist:

• Followed the style guidelines of this project

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[harmony7]

Looks like this was fixed, at least for the project that is important for us, by #2952. The other one is probably still a problem, but not blocking for us.