BaseTools: Split WorkspaceAutoGen._InitWorker into multiple functions

BaseTools: Split WorkspaceAutoGen._InitWorker into multiple functions

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1875

The WorkspaceAutoGen.__InitWorker function is too long, it's hard
to read and understand.
This patch is to separate the __InitWorker into multiple small ones.

Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Bob Feng <bob.c.feng@intel.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Liming Gao <liming.gao@intel.com>