Fix a bug where thin strokes be used when the setting was "dark background" or...

Fix a bug where thin strokes be used when the setting was "dark background" or "retina + dark background" even when the background was light because the background color didn't get passed through since we dididn't want to split up ligatures on background color changes. Since the thin strokes setting means the foreground depends on the background, the background color must be passed through and ligatures will be broken if the background color changes within them. Issue 6027

sources/iTermTextDrawingHelper.m

@@ -387,7 +387,7 @@ typedef struct iTermTextColorContext {
     // Now iterate over the lines and paint the characters.
     CGContextRef ctx = (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort];
-    if (self.minimumContrast > 0 || self.colorMap.mutingAmount > 0 || self.colorMap.dimmingAmount > 0) {
+    if ([self textAppearanceDependsOnBackgroundColor]) {
         [self drawForegroundForBackgroundRunArrays:backgroundRunArrays
                                                ctx:ctx];
     } else {
@@ -419,6 +419,25 @@ typedef struct iTermTextColorContext {
     }
 }
+- (BOOL)textAppearanceDependsOnBackgroundColor {
+    if (self.minimumContrast > 0) {
+        return YES;
+    }
+    if (self.colorMap.mutingAmount > 0) {
+        return YES;
+    }
+    if (self.colorMap.dimmingAmount > 0) {
+        return YES;
+    }
+    if (self.thinStrokes == iTermThinStrokesSettingDarkBackgroundsOnly) {
+        return YES;
+    }
+    if (self.thinStrokes == iTermThinStrokesSettingRetinaDarkBackgroundsOnly && _isRetina) {
+        return YES;
+    }
+    return NO;
+}
+
 #pragma mark - Drawing: Background
 - (void)drawBackgroundForLine:(int)line