…se instead of latest_revision:true (elastic#263717)

## Summary

Fixes the `latest_revision` filter used when listing and counting
package policies. The previous filter (`latest_revision:true`) excluded
8.x policies that never had `latest_revision` persisted to
Elasticsearch, causing them to appear with a count of 0 in the Installed
Integrations list after upgrading from 8.x to 9.x.

The fix changes all filters from `latest_revision:true` to `NOT
latest_revision:false`. This treats a missing field as equivalent to
`true` (i.e. a current revision), which is the correct semantic — a
policy without the field is a current revision, not a previous one.

### Root cause

The `latest_revision` field was introduced in SO model version 19
(package rollback feature, PR elastic#222779). For policies created in 8.x, the
field is absent in ES because:
- The v2 migration backfill only runs on one node in a multi-node
cluster; other nodes skip document transforms
- Patch upgrades (e.g. 9.2.7 → 9.2.8) skip the backfill entirely since
no outdated documents exist
- The list aggregation uses `perPage: 0`, bypassing the read-time
in-memory backfill path entirely

### Changes

- **`package_policies_aggregation.ts`** (Bug 1 + Bug 2): Change filter
to `NOT :false`; add `size: SO_SEARCH_LIMIT` to terms aggregation to
prevent ES default truncation at 10 buckets
- **`services/epm/packages/get.ts`** (Bug 3): Add `NOT
latest_revision:false` to `getPackageUsageStats` so `:prev` rollback
docs are excluded from stats counts
- **`services/package_policy.ts`**: Apply same filter fix to `list()`,
`listIds()`, `getAllItemsIds()`, `getCompiledVersionsForAgentPolicy()`,
and `findAllForAgentPolicy()`

Closes elastic#262491
Closes elastic/ingest-dev#7478

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Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
(cherry picked from commit 222e630)