Source maps in the npm package reference nonexistent files

Versions

0.3.4

Describe the bug

The source map comments included in the npm package point to source files that don't exist in the package. For example, build/module/index.js has the following contents:

import Plausible from './lib/tracker';
export default Plausible;
//# sourceMappingURL=data:application/json;base64,eyJ2ZXJzaW9uIjozLCJmaWxlIjoiaW5kZXguanMiLCJzb3VyY2VSb290IjoiIiwic291cmNlcyI6WyIuLi8uLi9zcmMvaW5kZXgudHMiXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6IkFBQUEsT0FBTyxTQUFTLE1BQU0sZUFBZSxDQUFDO0FBSXRDLGVBQWUsU0FBUyxDQUFDIn0=

sourceMappingURL decodes to this JSON:

{"version":3,"file":"index.js","sourceRoot":"","sources":["../../src/index.ts"],"names":[],"mappings":"AAAA,OAAO,SAAS,MAAM,eAAe,CAAC;AAItC,eAAe,SAAS,CAAC"}

which indicates that the original TypeScript source can be found at ../../src/index.ts. But the src/ directory doesn't exist at all in the package! This causes a warning from source-map-loader when run from a downstream packages and makes this code harder to debug.

Expected behavior

The source maps should be well-formed: either they should refer to files that exist or they should embed the TypeScript source directly using a "sourcesContent" key.

Steps to reproduce

Add plausible-tracker 0.3.4 as a dependency to a project that runs source-map-loader as part of its build.
Build that project.
Observe three warnings like the following are printed.

WARNING in ./node_modules/plausible-tracker/build/module/index.js
Module Warning (from ./node_modules/source-map-loader/dist/cjs.js):
Failed to parse source map from '.../node_modules/plausible-tracker/src/index.ts' file: Error: ENOENT: no such file or directory, open '.../node_modules/plausible-tracker/src/index.ts'
 @ ./src/analytics/plausible.ts 3:0-42 11:29-38
 @ ./src/index.tsx 8:0-55 13:0-14

plausible / plausible-tracker