GH-1962 - Fix Flyway migration discovery for dotted module identifiers.

[zemiles]

Fixes #1962.

HasMigrationFiles filters application modules before their Flyway locations are constructed. For a dotted identifier such as fully.qualified, it currently searches db/migration/fully.qualified, although the existing location customizer converts the identifier to db/migration/fully/qualified. The module can therefore be discarded before that correctly constructed location is used.

Apply the same dot-to-slash conversion in the migration-file check. This keeps discovery consistent with the existing location construction and limits the change to the filter.

The regression test places a migration resource under db/migration/fully/qualified and expects both the root and module configurations, with the module location set to classpath:db/migration/fully/qualified. Before the fix, the module is filtered out and only the root configuration remains. This test checks resource discovery and location configuration; it does not execute SQL migrations.

Validation on Windows with Oracle JDK 17.0.12:

• All 28 Runtime tests passed, including all 7 Flyway customizer tests.
• Full clean verify with -fae and build caching disabled failed in 6 existing JDBC findsPublicationsOlderThanReference assertions for Oracle and SQL Server (expected 1 result, got 2). Maven skipped 8 dependent modules. Those failures were not compared against an unchanged base branch.