Add reset text attributes function to GAL - use for arc tool

Independent drawing functions (that don't expect any particular state to
be set up fo them) on the GAL need to reset the GAL properties they
use. This adds GAL::ResetTextAttributes() to make this easier.

This is important, as failing to reset mirroring can cause asserts in
OpenGL.

This is used in the Ruler tool (which previously did it one attribute at
a time) and also the Arc layout assistant, which previously failed to
reset mirroring.

Also reset on GAL construction, as these members appear to be
uninitialised.

common/gal/graphics_abstraction_layer.cpp

@@ -70,6 +70,9 @@ GAL::GAL( GAL_DISPLAY_OPTIONS& aDisplayOptions ) :
     forceDisplayCursor = false;
     SetCursorEnabled( false );
 
+    // Initialize text properties
+    ResetTextAttributes();
+
     strokeFont.LoadNewStrokeFont( newstroke_font, newstroke_font_bufsize );
 
     // subscribe for settings updates
@@ -147,6 +150,21 @@ void GAL::SetTextAttributes( const EDA_TEXT* aText )
 }
 
 
+void GAL::ResetTextAttributes()
+{
+     // Tiny but non-zero - this will always need setting
+     // there is no built-in default
+    SetGlyphSize( { 1.0, 1.0 } );
+
+    SetHorizontalJustify( GR_TEXT_HJUSTIFY_CENTER );
+    SetVerticalJustify( GR_TEXT_VJUSTIFY_CENTER );
+
+    SetFontBold( false );
+    SetFontItalic( false );
+    SetTextMirrored( false );
+}
+
+
 VECTOR2D GAL::GetTextLineSize( const UTF8& aText ) const
 {
     // Compute the X and Y size of a given text.

common/preview_items/arc_assistant.cpp

@@ -131,6 +131,8 @@ void ARC_ASSISTANT::ViewDraw( int aLayer, KIGFX::VIEW* aView ) const
     gal.SetIsStroke( true );
     gal.SetIsFill( true );
 
+    gal.ResetTextAttributes();
+
     // constant text size on screen
     SetConstantGlyphHeight( gal, 12.0 );
 

common/preview_items/ruler_item.cpp

@@ -238,9 +238,8 @@ void RULER_ITEM::ViewDraw( int aLayer, KIGFX::VIEW* aView ) const
     gal.SetIsStroke( true );
     gal.SetIsFill( false );
     gal.SetStrokeColor( PreviewOverlayDefaultColor() );
-    gal.SetFontBold( false );
-    gal.SetFontItalic( false );
-    gal.SetTextMirrored( false );
+
+    gal.ResetTextAttributes();
 
     // draw the main line from the origin to cursor
     gal.DrawLine( origin, end );

include/gal/graphics_abstraction_layer.h

@@ -361,6 +361,14 @@ public:
      */
     virtual void SetTextAttributes( const EDA_TEXT* aText );
 
+    /**
+     * Reset text attributes to default styling
+     *
+     * Normally, custom attributes will be set individually after this,
+     * otherwise you can use SetTextAttributes()
+     */
+    void ResetTextAttributes();
+
     /**
      * @brief Set the font glyph size.
      *