tests: Add Wycheproof ECDH vectors

Adds a test for the ECDH module using the Wycheproof vectors.
We use a python script to convert the JSON-formatted vectors
into C code, in the same spirit as https://github.com/bitcoin-core/secp256k1/pull/1245

Co-authored-by: Sean Andersen <6730974+andozw@users.noreply.github.com>

src/wycheproof/WYCHEPROOF_COPYING

@@ -3,9 +3,18 @@
   `b063b4aedae951c69df014cd25fa6d69ae9e8cb9`, see
   https://github.com/google/wycheproof/blob/b063b4aedae951c69df014cd25fa6d69ae9e8cb9/testvectors_v1/ecdsa_secp256k1_sha256_bitcoin_test.json
 
+* The file `ecdh_secp256k1_test.json` in this directory
+  comes from Google's project Wycheproof with git commit
+  `d9f6ec7d8bd8c96da05368999094e4a75ba5cb3d`, see
+  https://github.com/google/wycheproof/blob/d9f6ec7d8bd8c96da05368999094e4a75ba5cb3d/testvectors_v1/ecdh_secp256k1_test.json
+
 * The file `ecdsa_secp256k1_sha256_bitcoin_test.h` is generated from
   `ecdsa_secp256k1_sha256_bitcoin_test.json` using the script
-  `tests_wycheproof_generate.py`.
+  `tests_wycheproof_generate_ecdsa.py`.
+
+* The file `ecdh_secp256k1_test.h` is generated from
+  `ecdh_secp256k1_test.json` using the script
+  `tests_wycheproof_generate_ecdh.py`.
 
 -------------------------------------------------------------------------------
 

src/wycheproof/ecdsa_secp256k1_sha256_bitcoin_test.h

@@ -1,4 +1,4 @@
-/* Note: this file was autogenerated using tests_wycheproof_generate.py. Do not edit. */
+/* Note: this file was autogenerated using tests_wycheproof_generate_ecdsa.py. Do not edit. */
 #define SECP256K1_ECDSA_WYCHEPROOF_NUMBER_TESTVECTORS (463)
 
 typedef struct {