Add Dart Map .map() term documentation

This pull request adds a new term entry for the Dart Map.map() method.

The entry explains how .map() transforms each key-value pair of a map into a new map using a provided function. It includes a clear syntax section and a simple example demonstrating the method in use, following Codecademy Docs content standards and writing guidelines.

This addition helps learners better understand how to work with Dart maps in a clear and beginner-friendly way.

Author: omkarhole

content/dart/concepts/map/terms/map/map.md

@@ -0,0 +1,87 @@
+---
+Title: 'Map.map()'
+Description: 'Map.map() transforms each key-value pair in a Dart Map into a new Map.'
+Subjects:
+  - 'Computer Science'
+  - 'Web Development'
+Tags:
+  - 'Dart'
+  - 'Data Structures'
+  - 'Methods'
+CatalogContent:
+  - 'learn-dart'
+  - 'paths/computer-science'
+---
+
+In Dart, the `.map()` method is used to create a new map by transforming each key-value pair of an existing map using a provided function.
+
+## Syntax
+
+```pseudo
+myMap.map((key, value) => MapEntry(newKey, newValue))
+```
+
+- `myMap`: The map whose entries are to be transformed.
+- `key`: The key from the original map.
+- `value`: The value associated with the key.
+- `MapEntry`: Represents a single key-value pair in the new map.
+
+## Example 1
+
+In the following example, the `.map()` method is used to create a new map by increasing each value by 1:
+
+```dart
+void main() {
+  Map<String, int> myMap = {
+    'a': 1,
+    'b': 2,
+    'c': 3
+  };
+
+  print('Original Map: $myMap');
+
+  // Using .map() to increase each value by 1
+  Map<String, int> newMap = myMap.map(
+    (key, value) => MapEntry(key, value + 1)
+  );
+
+  print('New Map after using .map(): $newMap');
+}
+```
+
+Here is the output for the above example:
+
+```shell
+Original Map: {a: 1, b: 2, c: 3}
+New Map after using .map(): {a: 2, b: 3, c: 4}
+```
+
+## Example 2
+
+In the following example, the `.map()` method is used to convert all values in a map to uppercase:
+
+```dart
+void main() {
+  Map<String, String> myMap = {
+    'x': 'apple',
+    'y': 'banana',
+    'z': 'cherry'
+  };
+
+  print('Original Map: $myMap');
+
+  // Using .map() to convert values to uppercase
+  Map<String, String> newMap = myMap.map(
+    (key, value) => MapEntry(key, value.toUpperCase())
+  );
+
+  print('New Map after using .map(): $newMap');
+}
+```
+
+Here is the output for the above example:
+
+```shell
+Original Map: {x: apple, y: banana, z: cherry}
+New Map after using .map(): {x: APPLE, y: BANANA, z: CHERRY}
+```