Add Dark Mode support for MR widget empty state icon

Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/330195

app/assets/stylesheets/startup/startup-dark.scss

@@ -1777,6 +1777,11 @@ body.gl-dark {
   --purple-800: #cbbbf2;
   --purple-900: #e1d8f9;
   --purple-950: #f4f0ff;
+  --dark-icon-color-purple-1: #524a68;
+  --dark-icon-color-purple-2: #715bae;
+  --dark-icon-color-purple-3: #9a79f7;
+  --dark-icon-color-orange-1: #665349;
+  --dark-icon-color-orange-2: #b37a5d;
   --gl-text-color: #fafafa;
   --border-color: #4f4f4f;
   --white: #333;
@@ -2003,6 +2008,11 @@ body.gl-dark {
   --purple-800: #cbbbf2;
   --purple-900: #e1d8f9;
   --purple-950: #f4f0ff;
+  --dark-icon-color-purple-1: #524a68;
+  --dark-icon-color-purple-2: #715bae;
+  --dark-icon-color-purple-3: #9a79f7;
+  --dark-icon-color-orange-1: #665349;
+  --dark-icon-color-orange-2: #b37a5d;
   --gl-text-color: #fafafa;
   --border-color: #4f4f4f;
   --white: #333;

app/assets/stylesheets/themes/_dark.scss

@@ -188,6 +188,12 @@ body.gl-dark {
   --purple-900: #{$purple-900};
   --purple-950: #{$purple-950};
 
+  --dark-icon-color-purple-1: #524a68;
+  --dark-icon-color-purple-2: #715bae;
+  --dark-icon-color-purple-3: #9a79f7;
+  --dark-icon-color-orange-1: #665349;
+  --dark-icon-color-orange-2: #b37a5d;
+
   --gl-text-color: #{$gray-900};
   --border-color: #{$border-color};
 

ee/app/assets/stylesheets/startup/startup-dark.scss

@@ -1777,6 +1777,11 @@ body.gl-dark {
   --purple-800: #cbbbf2;
   --purple-900: #e1d8f9;
   --purple-950: #f4f0ff;
+  --dark-icon-color-purple-1: #524a68;
+  --dark-icon-color-purple-2: #715bae;
+  --dark-icon-color-purple-3: #9a79f7;
+  --dark-icon-color-orange-1: #665349;
+  --dark-icon-color-orange-2: #b37a5d;
   --gl-text-color: #fafafa;
   --border-color: #4f4f4f;
   --white: #333;
@@ -2003,6 +2008,11 @@ body.gl-dark {
   --purple-800: #cbbbf2;
   --purple-900: #e1d8f9;
   --purple-950: #f4f0ff;
+  --dark-icon-color-purple-1: #524a68;
+  --dark-icon-color-purple-2: #715bae;
+  --dark-icon-color-purple-3: #9a79f7;
+  --dark-icon-color-orange-1: #665349;
+  --dark-icon-color-orange-2: #b37a5d;
   --gl-text-color: #fafafa;
   --border-color: #4f4f4f;
   --white: #333;