Generic TransactionSignatureCreator works with both CTransaction and CMutableTransaction

Summary:
Templated version so that no copying of CMutableTransaction into a CTransaction is
necessary. This speeds up the test case transaction_tests/test_big_witness_transaction
from 7.9 seconds to 3.1 seconds on my machine.

This is a backport of Core PR13309

Test Plan:

make check
./src/bench/bench_bitcoin

Reviewers: #bitcoin_abc, jasonbcox, Fabien

Reviewed By: #bitcoin_abc, jasonbcox, Fabien

Subscribers: Fabien, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D4200