Units: add support for light power units in Watt. Use for Eevee lights.

This affects point, spot and area lights. Sun light strength remains without
a unit. This change does not affect .blend file compatibility in any way, as
with the rest of the unit system it's purely a display and editing feature.

Not used for Cycles yet, that will be done after unifying the settings with
Eevee.

source/blender/python/intern/bpy_props.c

@@ -131,6 +131,7 @@ static const EnumPropertyItem property_subtype_array_items[] = {
 	{PROP_COLOR_GAMMA, "COLOR_GAMMA", 0, "Color Gamma", ""},
 	{PROP_LAYER, "LAYER", 0, "Layer", ""},
 	{PROP_LAYER_MEMBER, "LAYER_MEMBER", 0, "Layer Member", ""},
+	{PROP_POWER, "Power", 0, "Power", ""},
 
 	{PROP_NONE, "NONE", 0, "None", ""},
 	{0, NULL, 0, NULL, NULL},
@@ -139,7 +140,7 @@ static const EnumPropertyItem property_subtype_array_items[] = {
 #define BPY_PROPDEF_SUBTYPE_ARRAY_DOC \
 "   :arg subtype: Enumerator in ['COLOR', 'TRANSLATION', 'DIRECTION', " \
                                 "'VELOCITY', 'ACCELERATION', 'MATRIX', 'EULER', 'QUATERNION', 'AXISANGLE', " \
-                                "'XYZ', 'COLOR_GAMMA', 'LAYER', 'LAYER_MEMBER', 'NONE'].\n" \
+                                "'XYZ', 'COLOR_GAMMA', 'LAYER', 'LAYER_MEMBER', 'POWER', 'NONE'].\n" \
 "   :type subtype: string\n"
 
 /* PyObject's */
@@ -1902,7 +1903,7 @@ static void bpy_prop_callback_assign_enum(struct PropertyRNA *prop, PyObject *ge
 "   :type description: string\n" \
 
 #define BPY_PROPDEF_UNIT_DOC \
-"   :arg unit: Enumerator in ['NONE', 'LENGTH', 'AREA', 'VOLUME', 'ROTATION', 'TIME', 'VELOCITY', 'ACCELERATION', 'MASS', 'CAMERA'].\n" \
+"   :arg unit: Enumerator in ['NONE', 'LENGTH', 'AREA', 'VOLUME', 'ROTATION', 'TIME', 'VELOCITY', 'ACCELERATION', 'MASS', 'CAMERA', 'POWER'].\n" \
 "   :type unit: string\n" \
 
 #define BPY_PROPDEF_NUM_MIN_DOC \

source/blender/python/intern/bpy_utils_units.c

@@ -59,6 +59,7 @@ static const char *bpyunits_ucategorie_items[] = {
 	"VELOCITY",
 	"ACCELERATION",
 	"CAMERA",
+	"POWER",
 	NULL,
 };