Because the current restore has defined RestoreConfig, windows linker complains.
This commit rename the RestoreConfig used in FastRestore as RestoreConfigFR.
Add .h and .cpp files for RestoreLoader and RestoreApplier roles.
We will split the code for each restore role into a separate file.
This commit also fixes the bug in including RestoreCommon.actor.h, and
remove the unused code.
When we batch the mutations sent from loader to applier,
we forgot to clear the batch buffer in case of error,
which leads to undeterminism.
To fix the bug, we clear the mutation buffer before we use it.
We re-use some code from the existing restore system.
To make code review easier and code cleaner, we move the copied and
small-changed code into two separate files:
RestoreCommon.actor.h and RestoreCommon.actor.cpp
