[stats-log-api-gen] Rename vendor atom API to createVendorAtom

- aligned with java naming convention

Bug: 270167728
Test: stats-log-api-gen-test
Change-Id: I1bdb79d4857d55eaf4656594294e86755b2272ac
Merged-In: I1bdb79d4857d55eaf4656594294e86755b2272ac