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/004.txt

@@ -0,0 +1,36 @@
+From: Moderator-Address
+To: Recipient-List
+Date: Mon, 22 Mar 1994 13:34:51 +0000
+Subject: Internet Digest, volume 42
+MIME-Version: 1.0
+Content-Type: multipart/mixed;
+            boundary="---- main boundary ----"
+
+------ main boundary ----
+
+...Introductory text or table of contents...
+
+------ main boundary ----
+Content-Type: multipart/digest;
+            boundary="---- next message ----"
+
+------ next message ----
+
+From: someone-else
+Date: Fri, 26 Mar 1993 11:13:32 +0200
+Subject: my opinion
+
+...body goes here ...
+
+------ next message ----
+
+From: someone-else-again
+Date: Fri, 26 Mar 1993 10:07:13 -0500
+Subject: my different opinion
+
+... another body goes here ...
+
+------ next message ------
+
+------ main boundary ------
+