Merge bitcoin#13404: [tests] speed up of tx_validationcache_tests by reusing of CTransaction.

ebebedc speed up of tx_validationcache_tests by reusing of CTransaction. (lucash.dev@gmail.com)

Pull request description:

  The code was converting CMutableTransaction to CTransaction multiple times, which implies recalculating the hash multiple times. This commit fixes this by reusing a single CTransaction.

  Run-time results:
  ```
  Before:  6.7s
  After: 5.5s
  --------------
  Saved: 1.2s
  ```
  This PR was split from bitcoin#13050. Also, see bitcoin#10026.

Tree-SHA512: 61fb81972a08299085a7d3d0060485b265aefc7a4f82ab548e5f94371c8643cfb97bf0ef34f4e1211bf853d0217fa1c3338e4117f36fda1b37d203f690e86d60

Author: MarcoFalke

src/test/txvalidationcache_tests.cpp

@@ -114,7 +114,7 @@ BOOST_FIXTURE_TEST_CASE(tx_mempool_block_doublespend, TestChain100Setup)
 // should fail.
 // Capture this interaction with the upgraded_nop argument: set it when evaluating
 // any script flag that is implemented as an upgraded NOP code.
-static void ValidateCheckInputsForAllFlags(CMutableTransaction &tx, uint32_t failing_flags, bool add_to_cache)
+static void ValidateCheckInputsForAllFlags(const CTransaction &tx, uint32_t failing_flags, bool add_to_cache)
 {
     PrecomputedTransactionData txdata(tx);
     // If we add many more flags, this loop can get too expensive, but we can