mime/multipart: add helper to build content-disposition header contents
This PR adds an helper FileContentDisposition that builds multipart
Content-Disposition header contents with field name and file name,
escaping quotes and escape characters.
The function is then called in the related helper CreateFormFile.
The new function allows users to add other custom MIMEHeaders,
without having to rewrite the char escaping logic of field name and
file name, which is provided by the new helper.
Fixes #46771
Change-Id: Ifc82a79583feb6dd609ca1e6024e612fb58c05ce
GitHub-Last-Rev:
969f846fa967d2b3eca7a21ee096b299b8a94546
GitHub-Pull-Request: golang/go#63324
Reviewed-on: https://go-review.googlesource.com/c/go/+/531995
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>