Convert schema.inc to a service

Problem/Motivation

Convert the schema.inc functions to a service so it can be injected, unit tested and swapped. Affected functions:

• drupal_get_schema_versions()
• drupal_get_module_schema()
• drupal_schema_get_field_value()

The following functions should fall into the scope of extension services and should be moved in #2908886: Split off SchemaInstaller from schema.inc

• drupal_get_installed_schema_version()
• drupal_set_installed_schema_version()
• drupal_install_schema()
• drupal_uninstall_schema()
• _drupal_schema_initialize()

Already removed in https://www.drupal.org/node/2467521

• drupal_get_schema()
• drupal_get_complete_schema()
• drupal_get_schema_unprocessed()

Proposed resolution

Create a schema service with methods that replace the mentioned functions in schema.inc.

Remaining tasks

Deprecate the functions changed by this issue. https://www.drupal.org/core/deprecation#how-function

Move the extension-related functions into extension services. Follow-up or find child issue here: #2186491: [meta] D8 Extension System: Discovery/Listing/Info

User interface changes

None

API changes

New Schema service with the following methods:

• get
• getComplete
• getVersions
• getInstalledVersion
• setInstalledVersion
• install
• uninstall
• getUnprocessed
• getFieldsSqlgetFieldValue