Cleanup maxCount and showCharacterCount documentation.

Addresses questions about these comments when they synced to the open source release.
#225

PiperOrigin-RevId: 187925815

Author: nshahan

lib/material_input/base_material_input.dart

@@ -113,7 +113,7 @@ class BaseMaterialInput extends FocusableMixin
 
   /// Maximum allowed characters for character counting input box.
   ///
-  /// Always shows character count if the field is non-null.
+  /// Character count always is displayed when the value is non-null.
   @Input()
   int maxCount;
 
@@ -177,7 +177,7 @@ class BaseMaterialInput extends FocusableMixin
     }
   }
 
-  /// Displays character count even if maxCount is not defined.
+  /// Display character count even if maxCount is null.
   @Input()
   bool showCharacterCount = false;
 
@@ -434,7 +434,8 @@ class BaseMaterialInput extends FocusableMixin
 
   /// The message to display when character counter is shown.
   ///
-  /// Always shows [currentCount] but will ignore [maxCount] if it is null.
+  /// The character count in the form "[currentCount] / [maxCount]", such as
+  /// `12 / 25`, when [maxCount] is non-null; otherwise simply "[currentCount]".
   String msgCharacterCounter(int currentCount, int maxCount) => maxCount == null
       ? '$currentCount'
       : _msgCharacterCounter(currentCount, maxCount);

lib/material_input/material_input.dart

@@ -106,8 +106,8 @@ const String materialInputErrorKey = 'material-input-error';
 ///   character counter panel.
 /// - `rows` -- If the input is multiline, how many lines there are.
 /// - `maxRows` -- If the input is multiline, the max number of lines.
-/// - `showCharacterCount` -- Whether or not the character count will be
-///    displayed when maxCount is null.
+/// - `showCharacterCount` -- Force the character count to be displayed if
+///   maxCount is null.
 ///
 /// __Outputs:__
 ///