[flutter_markdown] Code decoration (#5060)

Because of using `DecoratedBox` for code block the content is above the decoration. This PR replaces `DecoratedBox` with `Container`.

![image](https://github.com/flutter/packages/assets/1847552/3203ecaf-23d3-44bd-ad73-f1369aa38020)

Issue: flutter/flutter#135858

Author: dawidope

packages/flutter_markdown/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.6.17+4
+
+* Fixes an issue where a code block would overlap its container decoration.
+
 ## 0.6.17+3
 
 * Fixes an incorrect note about SDK versions in the 0.6.17+2 CHANGELOG.md entry.

packages/flutter_markdown/lib/src/builder.dart

@@ -442,8 +442,9 @@ class MarkdownBuilder implements md.NodeVisitor {
           ),
         );
       } else if (tag == 'pre') {
-        child = DecoratedBox(
-          decoration: styleSheet.codeblockDecoration!,
+        child = Container(
+          clipBehavior: Clip.hardEdge,
+          decoration: styleSheet.codeblockDecoration,
           child: child,
         );
       } else if (tag == 'hr') {

packages/flutter_markdown/pubspec.yaml

@@ -4,7 +4,7 @@ description: A Markdown renderer for Flutter. Create rich text output,
   formatted with simple Markdown tags.
 repository: https://github.com/flutter/packages/tree/main/packages/flutter_markdown
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+flutter_markdown%22
-version: 0.6.17+3
+version: 0.6.17+4
 
 environment:
   sdk: ">=3.0.0 <4.0.0"