Support "--" end of options in SimpleCommandLineArgsParser

Prior to this commit, the `SimpleCommandLineArgsParser` would reject
"--" arguments as invalid. As reported by the community, the POSIX
utility conventions (Guideline 10) state that

> The first -- argument that is not an option-argument should be
> accepted as a delimiter indicating the end of options.
> Any following arguments should be treated as operands, even if they
> begin with the '-' character.

This commit updates `SimpleCommandLineArgsParser` to not reject "--"
arguments and instead to consider remaining arguments as non-optional.

See gh-31513

spring-core/src/test/java/org/springframework/core/env/SimpleCommandLineArgsParserTests.java

@@ -30,6 +30,7 @@ import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException
  *
  * @author Chris Beams
  * @author Sam Brannen
+ * @author Brian Clozel
  */
 class SimpleCommandLineArgsParserTests {
 
@@ -66,11 +67,6 @@ class SimpleCommandLineArgsParserTests {
 		assertThat(args.getOptionValues("o3")).isNull();
 	}
 
-	@Test
-	void withEmptyOptionText() {
-		assertThatIllegalArgumentException().isThrownBy(() -> parser.parse("--"));
-	}
-
 	@Test
 	void withEmptyOptionName() {
 		assertThatIllegalArgumentException().isThrownBy(() -> parser.parse("--=v1"));
@@ -112,4 +108,13 @@ class SimpleCommandLineArgsParserTests {
 				args.getNonOptionArgs().add("foo"));
 	}
 
+	@Test
+	void supportsEndOfOptionsDelimiter() {
+		CommandLineArgs args = parser.parse("--o1=v1", "--", "--o2=v2");
+		assertThat(args.containsOption("o1")).isTrue();
+		assertThat(args.containsOption("o2")).isFalse();
+		assertThat(args.getOptionValues("o1")).containsExactly("v1");
+		assertThat(args.getNonOptionArgs()).contains("--o2=v2");
+	}
+
 }