Add skip_row option to StaticMap

I think we should make the default to skip row instead of the fatal error. This also saves us having an extra configuration option.

I'm not really sure, but I think this is what is needed to skip rows by default.

It works for me. I'm using it for a use case in my migration on #2225293: Migrate D6 and D7 language negotiation settings

Looks good to me

+++ b/core/modules/migrate/lib/Drupal/migrate/Plugin/migrate/process/StaticMap.php
@@ -46,7 +47,7 @@ public function transform($value, MigrateExecutable $migrate_executable, Row $ro
+        throw new MigrateSkipRowException(sprintf('Lookup of %s failed.', var_export($value, TRUE)));

We no longer need the sprintf() since the message isn't used anywhere.

Also, moving this into the core issue queue since it's a change in the migrate module which i'm trying to avoid in the sandbox unless it is specifically holding something up.

Ok, fixing it. But this patch is required for #2225293

Looks good. This is an API change for the default behaviour for migrations using the static map so we'll need to re-run all the tests in the sandbox too.

Back to RTBC.

Committed c1cf341 and pushed to 8.x. Thanks!