Import upstream v0.16.22, stripped

Upstream commit: 474dd0229cb20cf513036619781ed97bd8073c3f
Enterprise-only files removed or emptied: 63
Enterprise-only snippets removed: 117 in 50 files
Dangling module declarations removed: 5
Cargo edits turning enterprise off: 14
Verification: clean
Enterprise feature gates left for rebuilt features: 19 in 18 files

Produced by tools/fork/strip.py. The full report is in docs/fork/strip-reports/ on main.

tests/resources/imap/006.txt

@@ -0,0 +1,23 @@
+From: [email protected]
+To: [email protected]
+Subject: Multipart Email Example
+Content-Type: multipart/alternative; boundary="boundary-string"
+
+--boundary-string
+Content-Type: text/plain; charset="utf-8"
+Content-Transfer-Encoding: quoted-printable
+Content-Disposition: inline
+
+Plain text email goes here!
+This is the fallback if email client does not support HTML
+
+--boundary-string
+Content-Type: text/html; charset="utf-8"
+Content-Transfer-Encoding: quoted-printable
+Content-Disposition: inline
+
+<h1>This is the HTML Section!</h1>
+<p>This is what displays in most modern email clients</p>
+
+--boundary-string--
+