According to RFC 2046, the BNF of the form data body is:
multipart-body := [preamble CRLF]
dash-boundary transport-padding CRLF
body-part *encapsulation
close-delimiter transport-padding
[CRLF epilogue]
Where "epilogue" is any text that "may be ignored or discarded". So we
should stop parsing the body once we encounter the terminating delimiter
("--").
Note that our parsing function is from an attempt to standardize the
grammar in the spec: https://andreubotella.github.io/multipart-form-data
This proposal hasn't been updated in ~4 years, and the fetch spec still
does not have a formal definition of the body string.
This patch ensure Headers object's associated header list
is ISO-8859-1 encoded when set using `Infra::isomorphic_encode`,
and correctly decoded using `Infra::isomorphic_decode`.
Follow-up of https://github.com/LadybirdBrowser/ladybird/pull/1893
The events tested here are decidedly async. We also can't really write
sync tests of the form "test(async () => {})". Nothing will await the
async callback.
