A dependency of a dependency of an assumeutxo related backport uses `IsPruneMode`, so let's backport these getters.
There are some callsites in init.cpp missing in this diff due to a missing backport related to a warning when the disk space is low.There is no risk of breaking anything if this is backported later and it does not seem very important.
> Add BlockManager::LoadingBlocks()
https://github.com/bitcoin/bitcoin/pull/26900/commits/fa0f0436d83288262d7d764b1d239c1a6de6146f
> Add BlockManager::GetPruneTarget()
https://github.com/bitcoin/bitcoin/pull/26900/commits/fae71fe27ec021583aaeac09aa924522bb63db05
> Add BlockManager::IsPruneMode()
https://github.com/bitcoin/bitcoin/pull/26900/commits/faf7b4f1fc35f1488567e0e4a57ecb348596b992
This is a backport of core#26900