Merge #13258: uint256: Remove unnecessary crypto/common.h dependency

bf2e01097 uint256: Remove unnecessary crypto/common.h use (Karl-Johan Alm)

Pull request description:

  This is an alternative to #13242 which keeps the `ReadLE64` part, but moves the `crypto/common.h` dependency into `crypto/common.h` as a function outside of `uint256`.

  **Reason:** this change will remove dependencies for `uint256` to `crypto/common.h`, `compat/endian.h`, and `compat/byteswap.h`.

  This PR removes the need to update tests to be endian-aware/-independent, but keeps the (arguably dubious) `ReadLE64` part (which was only introduced to fix the tests, not for any functionality).

Tree-SHA512: 78b35123cdb185b3b3ec59aba5ca8a5db72624d147f2d6a5484ffa5ce626a72f782a01dc6893fc8f5619b03e2eae7b5a03b0df5d43460f3bda428e719e188aec

src/hash.h

@@ -6,6 +6,7 @@
 #ifndef BITCOIN_HASH_H
 #define BITCOIN_HASH_H
 
+#include <crypto/common.h>
 #include <crypto/ripemd160.h>
 #include <crypto/sha256.h>
 #include <prevector.h>
@@ -138,6 +139,15 @@ public:
         return result;
     }
 
+    /**
+     * Returns the first 64 bits from the resulting hash.
+     */
+    inline uint64_t GetCheapHash() {
+        unsigned char result[CHash256::OUTPUT_SIZE];
+        ctx.Finalize(result);
+        return ReadLE64(result);
+    }
+
     template<typename T>
     CHashWriter& operator<<(const T& obj) {
         // Serialize to this stream