In Markdown Javadoc, indent continuation lines for Javadoc block tags by +2 rather than +4.

The reason is that a +4 indentation could be interpreted as a Markdown [indented code block](https://spec.commonmark.org/0.31.2/#indented-code-blocks) in some circumstances.

PiperOrigin-RevId: 954951163

Author: eamonnmcmanus

core/src/main/java/com/google/googlejavaformat/java/javadoc/JavadocWriter.java

@@ -521,7 +521,7 @@ enum AutoIndent {
   private int innerIndent() {
     int innerIndent = continuingListItemStack.total() + continuingListStack.total();
     if (continuingFooterTag) {
-      innerIndent += 4;
+      innerIndent += classicJavadoc ? 4 : 2;
     }
     return innerIndent;
   }

core/src/test/java/com/google/googlejavaformat/java/JavadocFormattingTest.java

@@ -1980,17 +1980,15 @@ public void markdownBlockTagContinuationLines() {
 /// rather than +4.
 record Test(String foo) {}
 """;
-    // TODO(b/537488642): continuation lines should be +2 to avoid the bug here.
-    // The four-space indentation leads to the second paragraph being interpreted as a code block.
     String expected =
 """
 /// Something something something.
 ///
 /// @param foo a parameter with a long description that will need to be wrapped onto multiple lines,
-///     with each line being indented by the default amount for continuation lines in a block tag.
+///   with each line being indented by the default amount for continuation lines in a block tag.
 ///
-///     There is even a second paragraph which illustrates why the indentation should be +2 rather
-///     than +4.
+///   There is even a second paragraph which illustrates why the indentation should be +2 rather
+///   than +4.
 record Test(String foo) {}
 """;