Revert "Issue #2218039 by sun, dawehner: Render the maintenance/install page like any other HTML page."

Broke update.php.

This reverts commit 10b03890.

Issue #1709960 by Berdir, zserno, jessebeach | joachim: Declare a maximum length for entity and bundle machine names.

Issue #2231945 by visabhishek, cs_shadow, fran seva | tstoeckler: FieldableDatabaseEntityStorageTest.php is misnamed.

Issue #2002246 by tompagabor, floretan, lauriii, pakmanlh, rbomhof | pixelite: Capitalize operations links in the comment and taxonomy term admin UI.

Issue #2227687 by cs_shadow, Cottser: Slightly ugly error message if a module is incompatible with the version of core and the PHP version.

Issue #1081192 by wojtha, klausi, larowlan, nedjo, Heine: Verify peer on HTTPS if cURL available (but be careful of built-in cert bundles in the codebase).

Issue #2229931 by xjm, Berdir: Improve documentation related to config object filename component limits

Issue #2228921 by sun: Consolidate system.module + system.theme + system.theme.disabled into core.extension config.

Issue #2200333 by Xano: Content_translation_view_access() is invoked as a hook_ENTITY_TYPE_access() hook implementation.

Issue #2054011 by amateescu, pwolanin, dawehner, YesCT, tim.plunkett, blueminds, Berdir, das-peter, effulgentsia: Implement built-in support for internal URLs.

Issue #2174443 by mr.baileys, David_Rothstein: Add security hardening protection option for programmatic form submissions to Drupal 8 (and backport to Drupal 6?).

Issue #2166915 by ianthomas_uk, sun | plach: Remove uses of deprecated language functions in tests and procedural code.

Issue #2121175 by Codenator, tim.plunkett, cosmicdreams, jayeshanandani, grom358, ianthomas_uk, Xano: Remove usage of drupal_get_form().

Issue #1969108 by danblack, jhodgdon: INSTALL.mysql.txt does not mention CREATE TEMPORARY TABLES and it should.

Issue #2220757 by Karol Haltenberger, xjm, drifter, zserno: Limit length of Config:: to something <= 166 characters.

Issue #2130205 by damiankloip, rbayliss, olli: Unable to "Expose this filter to visitors, to allow them to change it".