don't parse lines starting with @ as KDoc tags if they're inside a Markdown code fence

#KT-11789 Fixed

compiler/testData/kdoc/lexer/codeBlocks.kt

@@ -0,0 +1,14 @@
+/**
+ * @foo This is text.
+ * ``` kotlin
+ * @foo This is code block.
+ * ```
+ * @foo This is text.
+ * ~~~
+ * @foo This is code block
+ * With multiple lines.
+ * ~~~
+ * @foo This is yet more text.
+ * ```
+ * @foo This is an unclosed code block.
+ */

compiler/testData/kdoc/lexer/codeBlocks.txt

@@ -0,0 +1,48 @@
+KDOC_START ('/**')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' ')
+KDOC_TAG_NAME ('@foo')
+WHITE_SPACE (' ')
+KDOC_TEXT ('This is text.')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' ``` kotlin')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' @foo This is code block.')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' ```')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' ')
+KDOC_TAG_NAME ('@foo')
+WHITE_SPACE (' ')
+KDOC_TEXT ('This is text.')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' ~~~')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' @foo This is code block')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' With multiple lines.')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' ~~~')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' ')
+KDOC_TAG_NAME ('@foo')
+WHITE_SPACE (' ')
+KDOC_TEXT ('This is yet more text.')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' ```')
+WHITE_SPACE ('\n ')
+KDOC_LEADING_ASTERISK ('*')
+KDOC_TEXT (' @foo This is an unclosed code block.')
+WHITE_SPACE ('\n ')
+KDOC_END ('*/')

compiler/testData/psi/kdoc/AtTags.kt

@@ -1,5 +1,8 @@
 /**
  * @tag
  * text @notATag
+ * ```
+ * @notATag and some description
+ * ```
  * @
  */

compiler/testData/psi/kdoc/AtTags.txt

@@ -16,6 +16,15 @@ JetFile: AtTags.kt
         PsiElement(KDOC_TEXT)(' text @notATag')
         PsiWhiteSpace('\n ')
         PsiElement(KDOC_LEADING_ASTERISK)('*')
+        PsiElement(KDOC_TEXT)(' ```')
+        PsiWhiteSpace('\n ')
+        PsiElement(KDOC_LEADING_ASTERISK)('*')
+        PsiElement(KDOC_TEXT)(' @notATag and some description')
+        PsiWhiteSpace('\n ')
+        PsiElement(KDOC_LEADING_ASTERISK)('*')
+        PsiElement(KDOC_TEXT)(' ```')
+        PsiWhiteSpace('\n ')
+        PsiElement(KDOC_LEADING_ASTERISK)('*')
         PsiElement(KDOC_TEXT)(' @')
     PsiWhiteSpace('\n ')
-    PsiElement(KDOC_END)('*/')
+    PsiElement(KDOC_END)('*/')