[meta] Move core hooks from system.api.php to core.api.php or other files

I feel like doing this today. I'll make a list of where I'm moving each hook...

Here is a giant patch... I realize it is going to be hard to review, so I've made a list of what I moved where. I suggest that this get reviewed, to see if you agree with my decisions, and then you can review the patch to verify that I put things where I said I did.

---- List of what was moved -- I've grouped them a bit, and put them into the files in this order:

hook_cron(), callback_queue_worker(), hook_queue_info(), hook_queue_info_alter() => core.api.php

hook_hook_info(), hook_module_implements_alter() ==> core.api.php
hook_module_preinstall(), hook_modules_installed(), hook_module_preuninstall(), hook_modules_uninstalled() ==> core.api.php
hook_install(), hook_uninstall(), hook_install_tasks(), hook_install_tasks_alter() ==> core.api.php
hook_update_N(), hook_update_dependencies(), hook_update_last_removed() ==> core.api.php
hook_updater_info(), hook_updater_info_alter() ==> core.api.php
hook_requirements() ==> core.api.php

hook_mail(), hook_mail_alter(), hook_mail_backend_info_alter() ==> core.api.php

hook_cache_flush(), hook_rebuild() ==> core.api.php

hook_schema(), hook_schema_alter(), hook_query_alter(), hook_query_TAG_alter() ==> core.api.php

hook_tokens(), hook_tokens_alter(), hook_token_info(), hook_token_info_alter() ==> core.api.php

hook_link_alter() ==> core.api.php

hook_config_import_steps_alter() ==> core.api.php

hook_stream_wrappers(), hook_stream_wrappers_alter() ==> Made a new file: core/modules/system/file.api.php
hook_file_download(), hook_file_url_alter() ==> file.api.php
hook_file_mimetype_mapping_alter() ==> file.api.php
hook_archiver_info_alter() ==> file.api.php
hook_filetransfer_info(), hook_filetransfer_info_alter() ==> file.api.php

hook_js_alter(), hook_library_info_alter(), hook_library_alter(), hook_css_alter() ==> theme.api.php
hook_element_info(), hook_element_info_alter() ==> theme.api.php [note this file is for both render and theme hooks]
hook_page_build(), hook_page_alter() ==> theme.api.php
hook_theme(), hook_theme_registry_alter(), hook_template_preprocess_default_variables_alter() ==> theme.api.php

hook_ajax_render_alter() ==> form.api.php
hook_form_alter(), hook_form_FORM_ID_alter(), hook_form_BASE_FORM_ID_alter() ==> form.api.php
hook_batch_alter() ==> form.api.php [the batch callbacks are already in this file]

hook_data_type_info_alter() ==> entity.api.php [note: technically this is TypedData and not Entity API, but they are closely related so I thought it should be there]

hook_menu_link_defaults_alter() ==> core/modules/menu_link/menu_link.api.php

hook_menu_local_tasks(), hook_menu_local_tasks_alter(), hook_local_tasks_alter(), hook_menu_local_actions_alter(), hook_contextual_links_alter(), hook_contextual_links_plugins_alter() ==> core.api.php
hook_system_breadcrumb_alter() ==> core.api.php

hook_permission ==> core/modules/user/user.api.php

hook_countries_alter() ==> language.api.php

-------- Not moved:

hook_system_info_alter() -- not moved -- appears to be used in system.module functions, at least for now.
hook_help() -- not moved -- used by the System Help block (system module) and Help page (help module).
hook_system_themes_page_alter() -- function for the System module Themes page

Sorry, previous patch missed the new file I added (file.api.php). New patch...

Add remaining tasks, including one Novice review task and one maybe not novice, to the issue summary.

Thank you very much for reviewing!

Do you think the destinations make sense, or do you think we need to get someone more familiar with the hooks to make that decision?

Thanks... I hope someone can review this before too long...

I think the chances of getting this whole thing into one reviewed/non-conflicting patch is fairly small.

So I'm going to break it up into several smaller issues instead. I'll file them; they'll appear here as child issues.

There are two to review:
#2307859: Move theme/render hooks from system.api.php to theme.api.php
#2307853: Move file-related hooks to new api.php file

I'll file others if these get done... they will start to conflict with each other.

All the child issues are done, but there are still hooks to be moved. I'll file some more child issues soon.

Just filed a new child issue:
#2469941: Move database-related hook docs from system.api.php to a new database.api.php file

Also updating issue summary with list of other hooks still to move.