[foreign] RFR 8221611: prepare jextract tests for generated header, static forwarder name pattern change

[Sundararajan Athijegannathan]

Please review.

Bug: https://bugs.openjdk.java.net/browse/JDK-8221611
Webrev: https://cr.openjdk.java.net/~sundar/8221611/webrev.00/

PS. I locally tried name pattern to be foo_h_ and foo_h (for header 
interface and static forwarder respectively). Only 11 tests with the 
current webrev. Tests that use computed name of generated 
classes/interfaces all pass before/after name pattern change.

Thanks,
-Sundar