Provide location information for missing/invalid schema resources

This commit ensures that the `Resource` description is provided when
a schema resource is missing, cannot be read, or is invalid.
This is useful when the application holds multiple schema files and
an error is thrown because of a particular file.

Close gh-307

Author: dugenkui03

spring-graphql/src/main/java/org/springframework/graphql/execution/DefaultGraphQlSourceBuilder.java

@@ -184,7 +184,7 @@ private void registerDefaultTypeResolver(TypeDefinitionRegistry registry, Runtim
 
 	private TypeDefinitionRegistry parseSchemaResource(Resource schemaResource) {
 		Assert.notNull(schemaResource, "'schemaResource' not provided");
-		Assert.isTrue(schemaResource.exists(), "'schemaResource' does not exist");
+		Assert.isTrue(schemaResource.exists(), "'schemaResource' must exist: " + schemaResource);
 		try {
 			try (InputStream inputStream = schemaResource.getInputStream()) {
 				return new SchemaParser().parse(inputStream);
@@ -193,6 +193,9 @@ private TypeDefinitionRegistry parseSchemaResource(Resource schemaResource) {
 		catch (IOException ex) {
 			throw new IllegalArgumentException("Failed to load schema resource: " + schemaResource);
 		}
+		catch (Exception ex) {
+			throw new IllegalStateException("Failed to parse schema resource: " + schemaResource, ex);
+		}
 	}
 
 	private GraphQLSchema applyTypeVisitors(GraphQLSchema schema) {