[Tabs] Correct MDCTabBarView behavior for contentInset. (#8512)

When `contentInset` is non-zero, MDCTabBarView was misplacing the tabs views.
This PR corrects the issue by making the following changes:

*  Clustered Fixed tabs now set the `contentSize` to fill the entire safe area
   bounds.
*  Justified tabs tabs now expand the `contentSize` to fill at least the entire safe
   area bounds.
*  Right-aligned tabs position tabs views only within the content area and no
   longer depend on the min-X position of the bounds.
*  Rendering the divider line at the end of `layoutSubviews` to handle cases
   where scrolling adjusted the X-offset of the bounds.

Fixes #8236

components/Tabs/src/TabBarView/MDCTabBarView.m

@@ -580,9 +580,6 @@ - (void)layoutSubviews {
     }
   }
 
-  self.bottomDividerView.frame =
-      CGRectMake(CGRectGetMinX(self.bounds), CGRectGetMaxY(self.bounds) - kBottomDividerHeight,
-                 CGRectGetWidth(self.bounds), kBottomDividerHeight);
   self.contentSize = [self calculatedContentSize];
   [self updateSelectionIndicatorToIndex:[self.items indexOfObject:self.selectedItem]];
 
@@ -598,6 +595,11 @@ - (void)layoutSubviews {
     }
     [self scrollUntilSelectedItemIsVisibleWithoutAnimation];
   }
+  // It's possible that after scrolling the minX of bounds could have changed. Positioning it last
+  // ensures that its frame matches the displayed content bounds.
+  self.bottomDividerView.frame =
+      CGRectMake(CGRectGetMinX(self.bounds), CGRectGetMaxY(self.bounds) - kBottomDividerHeight,
+                 CGRectGetWidth(self.bounds), kBottomDividerHeight);
 }
 
 - (void)traitCollectionDidChange:(UITraitCollection *)previousTraitCollection {
@@ -695,8 +697,7 @@ - (void)layoutSubviewsForFixedClusteredLayout:(MDCTabBarViewLayoutStyle)layoutSt
   // Right-aligned
   if ((isRTL && layoutStyle == MDCTabBarViewLayoutStyleFixedClusteredLeading) ||
       (!isRTL && layoutStyle == MDCTabBarViewLayoutStyleFixedClusteredTrailing)) {
-    itemViewOriginX = CGRectGetMinX([self availableBoundsForSubviewLayout]) +
-                      (contentSize.width - totalRequiredWidth);
+    itemViewOriginX = (contentSize.width - totalRequiredWidth);
   }
   // Centered
   else if (layoutStyle == MDCTabBarViewLayoutStyleFixedClusteredCentered) {
@@ -760,15 +761,28 @@ - (CGSize)intrinsicContentSize {
   }
 }
 
+/**
+ The content size of the tabs in their current layout style.
+
+ For @c FixedJustified:  The content size is the maximum of the bounds within the safe area or the
+                         intrinsic size of the tabs when all tabs have the widest tab's width.
+ For @c FixedClustered*: The bounds within the safe area. This ensures they are positionined
+                         accurately within the content area.
+ For @c Scrollable:      The intrinsic size size of the tabs.
+ */
 - (CGSize)calculatedContentSize {
   switch ([self effectiveLayoutStyle]) {
     case MDCTabBarViewLayoutStyleFixed: {
-      return [self intrinsicContentSizeForJustifiedLayout];
+      CGSize intrinsicContentSize = [self intrinsicContentSizeForJustifiedLayout];
+      CGSize boundsSize = CGSizeMake(CGRectGetWidth(self.bounds), CGRectGetHeight(self.bounds));
+
+      return CGSizeMake(MAX(boundsSize.width, intrinsicContentSize.width),
+                        MAX(boundsSize.height, intrinsicContentSize.height));
     }
     case MDCTabBarViewLayoutStyleFixedClusteredCentered:
     case MDCTabBarViewLayoutStyleFixedClusteredTrailing:
     case MDCTabBarViewLayoutStyleFixedClusteredLeading: {
-      return [self intrinsicContentSizeForClusteredLayout];
+      return [self availableSizeForSubviewLayout];
     }
     case MDCTabBarViewLayoutStyleScrollable: {
       return [self intrinsicContentSizeForScrollableLayout];