Handle null source mappings

[loewenheim]

In version 0.24.1, esbuild changed the way it generates source mappings. This is the relevant section of the changelog:

Source mappings may now contain null entries (https://github.com/evanw/esbuild/issues/3310, https://github.com/evanw/esbuild/issues/3878)

With this change, sources that result in an empty source map may now emit a null source mapping (i.e. one with a generated position but without a source index or original position). This change improves source map accuracy by fixing a problem where minified code from a source without any source mappings could potentially still be associated with a mapping from another source file earlier in the generated output on the same minified line. It manifests as nonsensical files in source mapped stack traces. Now the null mapping "resets" the source map so that any lookups into the minified code without any mappings resolves to null (which appears as the output file in stack traces) instead of the incorrect source file.

This change shouldn't affect anything in most situations. I'm only mentioning it in the release notes in case it introduces a bug with source mapping. It's part of a work-in-progress future feature that will let you omit certain unimportant files from the generated source map to reduce source map size.

This change is likely the source of https://github.com/getsentry/sentry-cli/issues/2372. We should figure out if we can/want to support these mappings.