Amend path_alias indexes with domain_id for faster lookups

Problem/Motivation

The domain_path module adds a domain_id base field to the path_alias entity. All queries in DomainAliasRepository filter by domain_id together with alias or path and langcode.

Core defines four composite indexes on the path_alias tables covering (alias|path, langcode, id, status). The entity system also creates a single-column index on domain_id (path_alias_field__domain_id__target_id). For domain-filtered queries, the database must either intersect two separate indexes or use one and filter the other column from the table — neither is optimal for a high-traffic code path like alias resolution.

By including domain_id in the composite indexes, a single index scan covers (alias|path, langcode, domain_id) together, eliminating the need for index merges or additional lookups.

Proposed resolution

Amend core's four existing indexes to insert domain_id after langcode, using an imperative approach (install/update/uninstall hooks):

The leftmost prefix (alias|path, langcode) is preserved so core's own queries still benefit from the index.

Implementation in domain_path.install:

• domain_path_install() — amends indexes on fresh install
• domain_path_update_10007() — amends indexes for existing installs
• domain_path_uninstall() — restores core's original indexes before the entity system drops the domain_id column

Remaining tasks

Review and commit.