Make icons smaller for tertiary buttons

These are typically visually smaller buttons, since they don't have an outline. It makes more sense to use the size of the text then, or something thereabouts.

Contributes to issue CURA-8565.

resources/qml/TertiaryButton.qml

@@ -16,4 +16,5 @@ Cura.ActionButton
     textDisabledColor: UM.Theme.getColor("action_button_disabled_text")
     hoverColor: "transparent"
     underlineTextOnHover: true
+    iconSize: UM.Theme.getSize("action_button_icon_small").height
 }

resources/themes/cura-light/theme.json

@@ -564,6 +564,7 @@
 
         "action_button": [15.0, 2.5],
         "action_button_icon": [1.5, 1.5],
+        "action_button_icon_small": [1.0, 1.0],
         "action_button_radius": [0.15, 0.15],
         "dialog_primary_button_padding": [3.0, 0],