Call RewindBlockIndex without cs_main held
This PR makes a number of improvements to the InvalidateBlock (invalidateblock RPC) and RewindBlockIndex functions, primarily around breaking up their long-term cs_main holding. In addition:
- They're made safely interruptible (bitcoind can be shutdown, and no progress in either will be lost, though if incomplete, invalidateblock won't continue after restart and will need to be called again)
- The validation queue is prevented from overflowing (meaning invalidateblock on a very old block will not drive bitcoind OOM) (see #14289).
- invalidateblock won't bother to move transactions back into the mempool after 10 blocks (optimization).
Partial Backport of Bitcoin Core PR15402 (commit 880ce7d):
Modified version of "Call RewindBlockIndex without cs_main held"
RewindBlockIndex function was removed on D4728, but the locks were moved in`AppInitMain` function.
- Build with Clang in Debug mode:
CXX=clang++ CC=clang cmake .. -D CMAKE_CXX_FLAGS="-Werror=thread-safety-analysis" -GNinja -DCMAKE_BUILD_TYPE=Debug ninja check
- Verify that the compiler has not emitted a thread-safety warning.
- Run the node: ./src/bitcoind -regtest
- Verify that text similar to "Assertion failed: lock ... not held ..." is not printed on stderr.
Reviewers: #bitcoin_abc, deadalnix, markblundeberg
Reviewed By: #bitcoin_abc, markblundeberg
Differential Revision: https://reviews.bitcoinabc.org/D4757