Update MDCAlertControllerView to more explicitly expose the differe…

…ntiated `contentInsets` that are used in the `M3C` variation of the component.

PiperOrigin-RevId: 579938835

components/Dialogs/src/MDCAlertControllerView.h

@@ -54,6 +54,16 @@
  */
 @property(nonatomic, assign) UIEdgeInsets contentInsets;
 
+/**
+ The edge insets around the content view (which includes the message, and the accessory view if it
+ is set) against the dialog edges or its neighbor elements, the title and the actions.
+
+ In GM3, the bottom content inset is not needed due to the top action inset provding 24 spacing.
+
+ Default value is UIEdgeInsets(top: 24, leading: 24, bottom: 0, trailing: 24).
+ */
+@property(nonatomic, assign) UIEdgeInsets M3CDialogContentInsets;
+
 /**
  The edge insets around the actions against the dialog edges and its neighbor, which could be any of
  the other elements: the message, accessory view, title, title icon or title icon view.

components/Dialogs/src/private/MDCAlertControllerView+Private.m

@@ -43,8 +43,6 @@
 
 static const CGFloat MDCDialogMessageOpacity = 0.54f;
 
-static const UIEdgeInsets M3CDialogContentInsets = (UIEdgeInsets){24.0f, 24.0f, 0.0f, 24.0f};
-
 /** KVO context for this file. */
 static char *const kKVOContextMDCAlertControllerViewPrivate =
     "kKVOContextMDCAlertControllerViewPrivate";
@@ -117,6 +115,7 @@ - (instancetype)initWithFrame:(CGRect)frame {
     self.titleInsets = UIEdgeInsetsMake(24.0f, 24.0f, 20.0f, 24.0f);
     self.contentInsets = UIEdgeInsetsMake(24.0f, 24.0f, 24.0f, 24.0f);
     self.actionsInsets = UIEdgeInsetsMake(8.0f, 8.0f, 8.0f, 8.0f);
+    self.M3CDialogContentInsets = UIEdgeInsetsMake(24.0f, 24.0f, 0.0f, 24.0f);
     self.M3CButtonActionsInsets = UIEdgeInsetsMake(24.0f, 24.0f, 24.0f, 24.0f);
     self.actionsHorizontalMargin = 8.0f;
     self.M3CButtonActionsVerticalMargin = 8.0f;
@@ -178,6 +177,13 @@ - (instancetype)initWithFrame:(CGRect)frame {
   return self;
 }
 
+- (UIEdgeInsets)contentInsets {
+  if (self.M3CButtonEnabled) {
+    return self.M3CDialogContentInsets;
+  }
+  return _contentInsets;
+}
+
 - (NSString *)title {
   return self.titleLabel.text;
 }
@@ -188,14 +194,6 @@ - (void)setTitle:(NSString *)title {
   [self setNeedsLayout];
 }
 
-- (void)setM3CButtonEnabled:(BOOL)M3CButtonEnabled {
-  if (M3CButtonEnabled) {
-    // Bottom content inset is not needed due to the top action inset.
-    self.contentInsets = M3CDialogContentInsets;
-  }
-  _M3CButtonEnabled = M3CButtonEnabled;
-}
-
 - (void)setBackgroundColor:(UIColor *_Nullable)backgroundColor {
   super.backgroundColor = backgroundColor;
   self.titleView.backgroundColor = backgroundColor;