Inline `sources` field in source maps when preparing files for upload

[lforst]

Currently, the plugins move all source maps and source files into a single folder to prepare them for uploading.

By moving the files we break the relative relationships of source maps to their source files, thus breaking the sources field of the source maps, thus preventing Sentry CLI from inlining the sources field inside sourcesContent.

When tackling this we cannot forget about the sourcesRoot field.