Issue #474004 by mdrummond, kim.pepper, Wim Leers, jibran, tim.plunkett, joachim | JohnAlbin: Add options to system menu block so primary and secondary menus can be blocks rather than variables.

Issue #2278541 by tim.plunkett, kim.pepper, Bojhan, EclipseGc: Refactor block visibility to use condition plugins.

Issue #2233787 by alexpott, xjm | tim.plunkett: Move default configuration into extension/config/install to clarify its purpose.

Issue #2158003 by Wim Leers, msonnabaum, effulgentsia, moshe weitzman: Remove Block Cache API in favor of blocks returning #cache with cache tags.

Issue #2080823 by alexpott, swentel, Wim Leers: Create API to discover content or config entities' soft dependencies and use this to present a confirm form on module uninstall.

Issue #2167623 by danilenko_dn, sidharthap, Nitesh Sethia, krishnan.n, aitiba, alexpott, ashwinikumar, Barrett, damiankloip, deepakaryan1988, foxtrotcharlie, ianthomas_uk, neetu morwani, nonsie, piyuesh23, Sharique, sivaji, sushantpaste, swentel, vijaycs85, YesCT: Add test for all default configuration to ensure schema exists and is correct.

Issue #2043527 followup by tim.plunkett: Fixed Theme name is included in block machine name but should be stored as a key instead.

Issue #2043527 by tim.plunkett, vijaycs85, dawehner: Fixed Theme name is included in block machine name but should be stored as a key instead.

Issue #1927608 by EclipseGc, tim.plunkett, effulgentsia: Remove the tight coupling between Block Plugins and Block Entities.

Issue #1875260 by Gábor Hojtsy, xjm, brantwynn, EclipseGc, Bojhan: Fixed Make the block title required and allow it to be hidden.

Issue #1871696 by tim.plunkett, xjm, sun, msonnabaum, EclipseGc: Convert block instances to configuration entities to resolve architectural issues.

Issue #1535868 by EclipseGc, tim.plunkett, xjm, Jody Lynn, sdboyer, naxoc, tizzo, effulgentsia, dawehner, disasm, beejeebus: Convert all blocks into plugins.