Add fuzzing harness for `CheckTransaction(...)`, `IsStandardTx(...)` and other `CTransaction` related functions.

**Testing this PR**

Run:

```
$ CC=clang CXX=clang++ ./configure --enable-fuzz --with-sanitizers=address,fuzzer,undefined
$ make
$ src/test/fuzz/transaction
…
# And to to quickly verify that the relevant code regions are triggered, that the
# fuzzing throughput seems reasonable, etc.
$ contrib/devtools/test_fuzzing_harnesses.sh '^transaction$'
```

`test_fuzzing_harnesses.sh` can be found in PR #17000.

export CC=clang CXX=clang++
../configure --enable-fuzz --with-sanitizers=fuzzer,address \
  --disable-wallet \
  --disable-bench \
  --with-utils=no \
  --with-daemon=no \
  --with-libs=no \
  --with-gui=no \
  --with-seeder=no
make
mkdir -p test/fuzz
cp ../test/fuzz/test_runner.py test/fuzz/
./test/fuzz/test_runner.py -l DEBUG <path_to_corpus>

cmake -GNinja .. -DENABLE_SANITIZERS="address;fuzzer" -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++
ninja bitcoin-fuzzers link-fuzz-test_runner.py
./test/fuzz/test_runner.py -l DEBUG <path_to_corpus>