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/test/validate-regulators-config_tests.cpp b/phosphor-regulators/test/validate-regulators-config_tests.cpp
index 10cd7ce..3bc52da 100644
--- a/phosphor-regulators/test/validate-regulators-config_tests.cpp
+++ b/phosphor-regulators/test/validate-regulators-config_tests.cpp
@@ -36,8 +36,8 @@
     expectJsonInvalid(configFileJson, expectedErrorMessage,                    \
                       expectedOutputMessage)
 
-using namespace phosphor::power::regulators;
 using json = nlohmann::json;
+using TemporaryFile = phosphor::power::util::TemporaryFile;
 
 const json validConfigFile = R"(
     {