Move TemporaryFile class to root directory

Source code that is shared across applications is located in the root
directory of the phosphor-power repository.

The TemporaryFile class was originally created for the
phosphor-regulators application.  However it is general purpose and is
now needed by the phosphor-power-sequencer application.

Move the TemporaryFile class to the root directory.  Update C++ files
that use the TemporaryFile class since it is now in a different
namespace.  Update affected meson.build files.

Change-Id: I6d18080d2436a5da87b7ab51ac003c503caa36a3
Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
diff --git a/phosphor-regulators/src/ffdc_file.hpp b/phosphor-regulators/src/ffdc_file.hpp
index 923f09e..8ee9db8 100644
--- a/phosphor-regulators/src/ffdc_file.hpp
+++ b/phosphor-regulators/src/ffdc_file.hpp
@@ -29,6 +29,7 @@
 using FFDCFormat =
     sdbusplus::xyz::openbmc_project::Logging::server::Create::FFDCFormat;
 using FileDescriptor = phosphor::power::util::FileDescriptor;
+using TemporaryFile = phosphor::power::util::TemporaryFile;
 
 /**
  * @class FFDCFile