Create regulators IfAction class

Create the IfAction class that implements the "if" action in the JSON
config file.

See phosphor-regulators/docs/config_file/if.md for more information on
the "if" action.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: I16d5ba7bb88b5baa8a5085168a8bd2dc75449e9b
diff --git a/phosphor-regulators/test/meson.build b/phosphor-regulators/test/meson.build
index 5a9eea0..1d261f7 100644
--- a/phosphor-regulators/test/meson.build
+++ b/phosphor-regulators/test/meson.build
@@ -12,6 +12,7 @@
     'actions/action_environment_tests.cpp',
     'actions/action_utils_tests.cpp',
     'actions/and_action_tests.cpp',
+    'actions/if_action_tests.cpp',
     'actions/not_action_tests.cpp',
     'actions/or_action_tests.cpp',
     'actions/run_rule_action_tests.cpp',