`DataTypeFactory::get` locks a mutex inside shared a context, there was a case when many threads were locked inside it

https://pastila.nl/?0043b3e6/c557368f4cf0eb87a3c6f2cc162bc693

It is not clear which thread locked the mutex for a long time. However, it may be possible to lock less inside `DataTypeFactory::get`.
{
    auto lock = getLock();
    return shared->mmap_cache;
}
void Context::dropMMappedFileCache() const
{
    auto lock = getLock();
    if (shared->mmap_cache)
        shared->mmap_cache->reset();
}
void Context::dropCaches() const
{
    auto lock = getLock();
    if (shared->uncompressed_cache)
        shared->uncompressed_cache->reset();
    if (shared->mark_cache)
        shared->mark_cache->reset();
    if (shared->index_uncompressed_cache)
        shared->index_uncompressed_cache->reset();
    if (shared->index_mark_cache)
        shared->index_mark_cache->reset();
    if (shared->mmap_cache)
        shared->mmap_cache->reset();
}
BackgroundSchedulePool & Context::getBufferFlushSchedulePool() const