Fix ResolvableType raw class isAssignable checks

Fix `isAssignable` for `ResolvableType.forRawClass` so that it can be
used with types backed by a `TypeVarible`. Prior to this commit the
rawClass value was used, which wouldn't always work.

Closes gh-23321

Author: philwebb

spring-core/src/main/java/org/springframework/core/ResolvableType.java

@@ -1015,7 +1015,7 @@ public boolean isAssignableFrom(Class<?> other) {
 			}
 			@Override
 			public boolean isAssignableFrom(ResolvableType other) {
-				Class<?> otherClass = other.getRawClass();
+				Class<?> otherClass = other.resolve();
 				return (otherClass != null && (clazz == null || ClassUtils.isAssignable(clazz, otherClass)));
 			}
 		};

spring-core/src/test/java/org/springframework/core/ResolvableTypeTests.java

@@ -135,6 +135,18 @@ public void forRawClassWithNull() throws Exception {
 		assertTrue(type.isAssignableFrom(String.class));
 	}
 
+	@Test
+	public void forRawClassAssignableFromTypeVariable() { // gh-23321
+		ResolvableType typeVariable = ResolvableType.forClass(ExtendsList.class).as(List.class).getGeneric();
+		ResolvableType raw = ResolvableType.forRawClass(CharSequence.class);
+		assertThat(raw.resolve()).isEqualTo(CharSequence.class);
+		assertThat(typeVariable.resolve()).isEqualTo(CharSequence.class);
+		assertThat(raw.resolve().isAssignableFrom(typeVariable.resolve())).isTrue();
+		assertThat(typeVariable.resolve().isAssignableFrom(raw.resolve())).isTrue();
+		assertThat(raw.isAssignableFrom(typeVariable)).isTrue();
+		assertThat(typeVariable.isAssignableFrom(raw)).isTrue();
+	}
+
 	@Test
 	public void forInstanceMustNotBeNull() {
 		this.thrown.expect(IllegalArgumentException.class);