Fix parsing failure for MIME types with quoted pairs

Prior to this commit, MIME types with parameter values that contain a
quoted pair would sometimes fail and parse an incomplete parameter
value.

This commit ensures that the quoted section of the parameter value is
correctly handled.

Fixes gh-36730

spring-core/src/main/java/org/springframework/util/MimeTypeUtils.java

@@ -238,7 +238,7 @@ public abstract class MimeTypeUtils {
 						break;
 					}
 				}
-				else if (ch == '"') {
+				else if (ch == '"' && mimeType.charAt(nextIndex - 1) != '\\') {
 					quoted = !quoted;
 				}
 				nextIndex++;

spring-core/src/test/java/org/springframework/util/MimeTypeTests.java

@@ -98,7 +98,7 @@ class MimeTypeTests {
 	}
 
 	@Test
-	void parseQuotedSeparator() {
+	void parseQuotedParameterValue() {
 		String s = "application/xop+xml;charset=utf-8;type=\"application/soap+xml;action=\\\"https://x.y.z\\\"\"";
 		MimeType mimeType = MimeType.valueOf(s);
 		assertThat(mimeType.getType()).as("Invalid type").isEqualTo("application");
@@ -107,6 +107,15 @@ class MimeTypeTests {
 		assertThat(mimeType.getParameter("type")).isEqualTo("\"application/soap+xml;action=\\\"https://x.y.z\\\"\"");
 	}
 
+	@Test
+	void parseParameterWithQuotedPair() {
+		String s = "text/plain;twelve=\"1\\\"2\"";
+		MimeType mimeType = MimeType.valueOf(s);
+		assertThat(mimeType.getType()).as("Invalid type").isEqualTo("text");
+		assertThat(mimeType.getSubtype()).as("Invalid subtype").isEqualTo("plain");
+		assertThat(mimeType.getParameter("twelve")).isEqualTo("\"1\\\"2\"");
+	}
+
 	@Test
 	void withConversionService() {
 		ConversionService conversionService = new DefaultConversionService();