[6.x] Add SQLite production support

[riasvdv]

Description

We've had SQLite running the full Unit & Feature suite alongside MySQL and Postgres for a bit now, this brings SQLite support to the remaining parts of the codebase like the installer.

I'd still consider it experimental support, but this at least allows people to experiment with it

[Copilot]

Pull request overview

This PR expands Craft CMS 6’s SQLite support beyond the test suite into production-facing flows (installer, setup commands, requirement checks), by centralizing SQLite-specific connection normalization and DSN/requirements-checker configuration.

Changes:

• Added ConnectionConfig to normalize SQLite connection configs (paths, pragmas, env-var cleanup, DSN generation) and to configure RequirementsChecker.
• Updated installer + CLI DB credential flows to support SQLite (including creating the DB file when appropriate and removing server-only env vars).
• Updated install UI to allow selecting SQLite/MariaDB and to use driver-specific defaults.

Reviewed changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
yii2-adapter/tests/unit/helpers/FileHelper/FileHelperTest.php	Adjusts a Windows path test case to align with updated absolute-path handling.
tests/Unit/Database/ConnectionConfigTest.php	Adds unit coverage for SQLite config normalization, path normalization, and DSN generation.
tests/Unit/Console/DatabaseCredentialsCommandTest.php	Adds a test ensuring SQLite credentials don’t persist server env vars.
tests/TestCase.php	Normalizes configured DB connections in tests and ensures SQLite DB files exist when needed.
tests/Feature/Http/Controllers/InstallControllerTest.php	Expands installer tests for SQLite defaults, validation, and file creation behavior.
src/Utility/Utilities/SystemReport.php	Switches requirements DSN/config generation to ConnectionConfig::requirementsChecker().
src/Support/File.php	Treats lowercase Windows drive letters as absolute paths.
src/Http/Middleware/CheckRequirements.php	Uses ConnectionConfig::requirementsChecker() instead of manually building DSNs.
src/Http/Controllers/Updates/UpdaterController.php	Uses ConnectionConfig::requirementsChecker() for server checks.
src/Http/Controllers/InstallController.php	Adds SQLite to supported drivers; adds driver defaults; validates/creates SQLite DB files; writes SQLite-appropriate env vars; handles db2 behavior for SQLite.
src/Database/DatabaseServiceProvider.php	Normalizes configured DB connections at registration; routes SQLite bulk ops to the default connection via ConnectionConfig.
src/Database/ConnectionConfig.php	New helper for SQLite normalization, path handling, DB file creation, requirements checker setup, and db2 bulk-ops wiring.
src/Console/Commands/Setup/DatabaseCredentialsCommand.php	Adds SQLite support to db-creds setup flow (prompts/env writing/testing/db2 handling).
src/Console/Commands/Install/InstallCommand.php	Uses the migration command class when invoking initial migrations.
resources/js/pages/install/Install.vue	Updates install form model to use driver defaults and pass them to DB fields.
resources/js/modules/install/components/InstallingScreen.vue	Switches install request to usePost + uses server-provided redirect URL.
resources/js/modules/install/components/DbFields.vue	Adds SQLite/MariaDB drivers and driver-specific field visibility/placeholders.
CHANGELOG.md	Notes addition of SQLite database support.