Add a way for Backend to signal scale changes

On Wayland the scale now changes to the correct value as the Tracy
window is moved across monitors.

If the scale is overridden from environment, it does not change, just
like before.

profiler/src/main.cpp

@@ -95,6 +95,7 @@ static ConnectionHistory* connHist;
 static std::atomic<ViewShutdown> viewShutdown { ViewShutdown::False };
 static double animTime = 0;
 static float dpiScale = 1.f;
+static bool dpiScaleOverriddenFromEnv = false;
 static Filters* filt;
 static RunQueue mainThreadTasks;
 static uint32_t updateVersion = 0;
@@ -197,6 +198,15 @@ static bool SaveConfig()
     return true;
 }
 
+static void ScaleChanged( float scale )
+{
+    if ( dpiScaleOverriddenFromEnv ) return;
+    if ( dpiScale == scale ) return;
+
+    dpiScale = scale;
+    SetupDPIScale( dpiScale, s_fixedWidth, s_bigFont, s_smallFont );
+}
+
 int main( int argc, char** argv )
 {
     sprintf( title, "Tracy Profiler %i.%i.%i", tracy::Version::Major, tracy::Version::Minor, tracy::Version::Patch );
@@ -279,7 +289,7 @@ int main( int argc, char** argv )
     LoadConfig();
 
     ImGuiTracyContext imguiContext;
-    Backend backend( title, DrawContents, &mainThreadTasks );
+    Backend backend( title, DrawContents, ScaleChanged, &mainThreadTasks );
     tracy::InitTexture();
     iconTex = tracy::MakeTexture();
     zigzagTex = tracy::MakeTexture( true );
@@ -292,7 +302,11 @@ int main( int argc, char** argv )
     if( envDpiScale )
     {
         const auto cnv = atof( envDpiScale );
-        if( cnv != 0 ) dpiScale = cnv;
+        if( cnv != 0 )
+        {
+            dpiScale = cnv;
+            dpiScaleOverriddenFromEnv = true;
+        }
     }
 
     SetupDPIScale( dpiScale, s_fixedWidth, s_bigFont, s_smallFont );