oe-build-perf-report: Add dark mode

Update css to add dark mode when window prefers-color-scheme is dark.

(From OE-Core rev: ed02a235d42202279ad5e4e3153247f9e5e2bba8)

Signed-off-by: Ninette Adhikari <ninette@thehoodiefirm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/build_perf/html/measurement_chart.html

@@ -81,13 +81,20 @@
 
   // Draw chart
   const chart_div = document.getElementById('{{ chart_elem_id }}');
-  const measurement_chart= echarts.init(chart_div, null, {
-    height: 320
-  });
+  // Set dark mode
+  let measurement_chart
+  if (window.matchMedia('(prefers-color-scheme: dark)').matches) {
+      measurement_chart= echarts.init(chart_div, 'dark', {
+      height: 320
+    });
+  } else {
+      measurement_chart= echarts.init(chart_div, null, {
+      height: 320
+    });
+  }
   // Change chart size with browser resize
   window.addEventListener('resize', function() {
     measurement_chart.resize();
   });
   measurement_chart.setOption(option);
 </script>
-