dist is both more accurate (the 'build' directory is normally where you do the build,
and normally consists of intermediate build artifacts no one cares about). dist also
occurs less frequently in the code base: after this change \bbuild\b has 466 matches,
whereas \bdist\b has 101 matches. build has 1072 matches whereas dist has 362.
If no indexURL is provided, we throw and catch an error and
then use ErrorStackParser to calculate where pyodide.js has
been loaded from. Resolves#2290.
Question: But getting the URL from error stack trace is well... really
hacky. Can't we use
[`document.currentScript`](https://developer.mozilla.org/en-US/docs/Web/API/Document/currentScript)
or
[`import.meta.url`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import.meta)
instead?
Answer: `document.currentScript` works for the browser main thread.
`import.meta` works for es6 modules. In a classic webworker, I think there
is no approach that works. Also we would need some third approach for node
when loading a commonjs module using `require`. On the other hand, this
stack trace approach works for every case without any feature detection
code.