Re-enable checkXDRFileIdentity and update p28 dep tree

The XDR identity check was commented out pending the p28 bump; this
commit does that bump, so re-enable it.

p28-expect.txt picks up the new stellar-xdr rev from the host repin. The
only change is the rev itself, in both places it appears; p21-p27 are
untouched.

Author: sisuresh

src/main/main.cpp

@@ -428,12 +428,7 @@ main(int argc, char* const* argv)
             Config::CURRENT_LEDGER_PROTOCOL_VERSION);
 
 #ifndef ENABLE_NEXT_PROTOCOL_VERSION_UNSAFE_FOR_PRODUCTION
-        // Disable the XDR check temporarily until p28 bump. Due to imperfect
-        // check mechanism, vCurr XDR has 'diverged' from p27 host XDR because
-        // we've moved some definitions around (even though there were no
-        // semantic changes).
-        // When we bump Core to p28, we should re-enable this check.
-        // checkXDRFileIdentity();
+        checkXDRFileIdentity();
 #endif
     }
     catch (...)

src/rust/src/dep-trees/p28-expect.txt

@@ -259,7 +259,7 @@ soroban-env-host v28.0.0 (src/rust/soroban/p28/soroban-env-host)
 │   │   │   ├── itoa v1.0.6
 │   │   │   ├── ryu v1.0.13
 │   │   │   └── serde v1.0.192 (*)
-│   │   ├── stellar-xdr v27.0.0 (https://github.com/stellar/rs-stellar-xdr?rev=a90de0c0d6eba8be668e9074cfb7b285ac0ecd34#a90de0c0)
+│   │   ├── stellar-xdr v27.0.0 (https://github.com/stellar/rs-stellar-xdr?rev=3305b3e31f19fdb4e64e4b7a4354bb120cdf4415#3305b3e3)
 │   │   │   ├── escape-bytes v0.1.1
 │   │   │   ├── ethnum v1.5.3
 │   │   │   ├── hex v0.4.3
@@ -289,7 +289,7 @@ soroban-env-host v28.0.0 (src/rust/soroban/p28/soroban-env-host)
 │   │   └── wasmparser-nostd v0.100.2
 │   │       └── indexmap-nostd v0.4.0
 │   ├── static_assertions v1.1.0
-│   ├── stellar-xdr v27.0.0 (https://github.com/stellar/rs-stellar-xdr?rev=a90de0c0d6eba8be668e9074cfb7b285ac0ecd34#a90de0c0)
+│   ├── stellar-xdr v27.0.0 (https://github.com/stellar/rs-stellar-xdr?rev=3305b3e31f19fdb4e64e4b7a4354bb120cdf4415#3305b3e3)
 │   │   ├── base64 v0.22.1
 │   │   ├── escape-bytes v0.1.1
 │   │   ├── ethnum v1.5.3