Import upstream v0.16.23, stripped

Upstream commit: 9d1c75ab68435e4417337f768291e5f947686203
Enterprise-only files removed or emptied: 63
Enterprise-only snippets removed: 118 in 50 files
Dangling module declarations removed: 5
Edits turning enterprise off: 25
Third-party code: 14 files, 0 not in THIRD-PARTY.md
Verification: clean

One snippet more than v0.16.22, in crates/common/src/auth/authentication.rs
(3, was 2).

crates/common/src/auth/oauth/token.rs

@@ -17,7 +17,7 @@ pub const FAILED_TO_DECODE_TOKEN: &str = concat!(
     "the Authentication object."
 );
 
-const TOKEN_HEADER: &str = "sw1.";
+pub(crate) const TOKEN_HEADER: &str = "sw1.";
 const TOKEN_KEY_CONTEXT: &str = "stalwart-oauth-token-sw1";
 const OAUTH_EPOCH: u64 = 946684800; // Jan 1, 2000