[GR-64061] Footprint improvements in Native Image Builder.

[graalvmbot]

Low-hanging fruits to improve memory footprint in the native image builder

• avoid new string creation in CEntryPointData, potentially empty string => in the range of thousands of empty strings saved, all using the same pointer now (via standard string interning.
• avoid duplicate but empty arrays => instead of allocating lots of T[0], have them all point to the same singleton object. Saving thousands of entries even in a helloworld; take care not to affect cases that use reference equality.
• clean CodeBreakdownProvider after usage => clean more of the provider earlier; larger save, but only affecting a few late steps.