task: #2934063 Remove installer extension pathname workaround

Andrey Postnikovrequested to merge
issue/drupal-2934063:2934063-rescoped into main

Remove the installer-specific static pathname workaround now that the base extension list resolves manually added pathnames. Drop the profile pathname priming from install_begin_request(), InstallStorage and ExtensionInstallStorage; resolve the active profile through the profile extension list in ConfigInstaller; and seed ModuleExtensionList added pathnames directly instead of through setPathname().

Stop NormalInstallerServiceProvider swapping in the installer-specific extension lists, and reduce InstallerModuleExtensionList, InstallerThemeExtensionList and ExtensionListTrait to deprecated backward-compatibility shims. Deprecate the now internal-only ExtensionList::setPathname().

Closes #2934063

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