### What problem does this PR solve?

Issue Number: N/A

Problem Summary:

Queries such as:

```sql
SELECT COUNT(*) FROM example_catalog.information_schema.schemata;
```

only need database and catalog names. However, `SchemaSchemataScanner`
uses the default `getDbNames` RPC, whose FE handler calls
`catalog.getAllDbs()` to also return database IDs. For external
catalogs, this resolves every database object even though SCHEMATA never
reads those IDs. A large namespace list can therefore churn a much
smaller database-object cache and allocate substantial temporary
metadata while waiting inside a synchronous BE-to-FE RPC. A warm
database-name cache does not remove this work.

This PR adds the optional `include_db_ids` request field, defaulting to
`true`, and lets SCHEMATA set it to `false`. The FE then calls
`catalog.getDbNames()` and omits the unused database IDs. Both paths
share the existing privilege checks, pattern matching, and schema-name
formatting. Callers that need IDs keep the object-enumeration path
without additional intermediate lists.

The new field uses ID 8; field 7 remains reserved. Definitions were
checked on master and branch-3.1/4.0/4.1/4.2. Older FE nodes ignore the
optional field and keep serving the existing response; older BE callers
retain the default ID-inclusive behavior on a new FE.

### Validation

- Added a 100,000-namespace test that rejects any database-object
enumeration and verifies the result-array lengths and omitted IDs.
- Covered privilege/pattern filtering, qualified schema names,
empty/unavailable catalogs, existing ID-returning callers, and binary
deserialization of requests without the new field.
- Confirmed the new behavior tests fail on the original handler before
implementing the change. All 7 targeted FE tests pass, including the
existing `FrontendServiceImplTest#testGetDBNames`.

```bash
bash run-fe-ut.sh --run 'org.apache.doris.service.FrontendServiceGetDbNamesTest,org.apache.doris.service.FrontendServiceImplTest#testGetDBNames'
```

- FE Checkstyle: passed with zero violations.
- Changed BE scanner: clang-format 16 and C++ syntax-only compilation
with regenerated Thrift headers passed.

An in-process FE-handler benchmark uses the actual `ExternalCatalog` /
`TestExternalCatalog` name and object-cache implementations, a synthetic
metadata provider, and stubbed catalog routing and privilege checks. It
compares the original handler source at master commit
`bdb90856e6e468eb495e5bfd67010de90570bfbc` with the patched handler,
using the same dependencies and fixture. Each trial starts with a warm
name cache and cold object cache, whose capacity is 1,000. There are
100,000 synthetic namespaces plus the two system databases. Settings:
JDK 17, 2 GiB heap, 4 active processors; discard one warm-up pair and
report medians from three measured trials.

| Metric | Original master | Patched SCHEMATA path |
| --- | ---: | ---: |
| FE handler elapsed time | 2,984.2 ms | 1,331.1 ms |
| Cumulative current-thread allocation | 2,117.2 MiB | 726.2 MiB |
| Database objects constructed | 100,002 | 0 |
| Name-provider invocations | 1 | 1 |
| Returned rows | 100,002 | 100,002 |

In this fixture, handler time falls by 55.4% (2.24x faster) and
cumulative allocation falls by 65.7%. Allocation is total bytes
allocated during the call, not peak live heap. This benchmark excludes
network transport, Thrift serialization, and SQL execution; it does not
measure a deployed PostgreSQL/Iceberg environment. Full BE linking and a
deployed end-to-end SQL test were not run locally.

### Release note

Improve `information_schema.schemata` enumeration for large catalogs by
avoiding unnecessary database-object loading.

### Check List (For Author)

- Test
    - [ ] Regression test
    - [x] Unit Test
    - [x] Manual test (FE-handler benchmark described above)
    - [ ] No need to test or manual test.
- Behavior changed:
- [x] No. SQL result semantics and existing ID-returning requests are
preserved.
    - [ ] Yes.
- Does this need documentation?
    - [x] No.
    - [ ] Yes.

### Check List (For Reviewer who merge this PR)

- [ ] Confirm the release note
- [ ] Confirm test cases
- [ ] Confirm document
- [ ] Add branch pick label