Cleanup: Grease Pencil: Correct stroke outline tooltip description

Replaced "Convert stroke to **perimeter**" with "Convert stroke to **outline**"
in the outline tooltip description.

It was suggested that the description is not accurate and could be misleading
between the two terms. Thus, I simply just replaced the word across all tooltip
descriptions to keep it consistent and easily understood.

Resolves #126814.

Pull Request: https://projects.blender.org/blender/blender/pulls/127990

source/blender/makesrna/intern/rna_brush.cc

@@ -1886,7 +1886,7 @@ static void rna_def_gpencil_options(BlenderRNA *brna)
   prop = RNA_def_property(srna, "use_settings_outline", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, nullptr, "flag", GP_BRUSH_OUTLINE_STROKE);
   RNA_def_property_boolean_default(prop, false);
-  RNA_def_property_ui_text(prop, "Outline", "Convert stroke to perimeter");
+  RNA_def_property_ui_text(prop, "Outline", "Convert stroke to outline");
   RNA_def_property_clear_flag(prop, PROP_ANIMATABLE);
 
   prop = RNA_def_property(srna, "use_edit_position", PROP_BOOLEAN, PROP_NONE);

source/blender/makesrna/intern/rna_modifier.cc

@@ -285,7 +285,7 @@ const EnumPropertyItem rna_enum_object_modifier_type_items[] = {
      "GREASE_PENCIL_OUTLINE",
      ICON_MOD_OUTLINE,
      "Outline",
-     "Convert stroke to perimeter"},
+     "Convert stroke to outline"},
 
     RNA_ENUM_ITEM_HEADING(N_("Deform"), nullptr),
     {eModifierType_Armature,