Issue #3061266 by smustgrave, Grimreaper, ridhimaabrol24, nod_, pavnish, ithom, Hardik_Patel_12, Webbeh, alexpott: Prefix block machine name suggestions with the theme machine name

Issue #2862564 by smustgrave, Manuel Garcia, ifrik, acbramley, amjad1233, benjifisher, manuel.adan, Anchal_gupta, tedbow, Lendude, yogeshmpawar, larowlan, rkoller, AaronMcHale, gambry, rachel_norfolk, yoroy, xjm, Webbeh, catch, mstrelan: Move Custom block library to Content

Issue #3044117 by e.escribano, segovia94, bkosborne, Webbeh, zterry95, tim.plunkett, emerham: Add getter for layout object in Layout Builder's ConfigureSectionForm

Issue #2957953 by alexpott, sleitner, pobster, Berdir, mohit_aghera, kishor_kolekar, joegraduate, trackleft2, bappa.sarkar, acbramley, ankithashetty, paulocs, batkor, dhirendra.mishra, seanB, priyanka.sahni, Abhijith S, chetanbharambe, vikashsoni, anmolgoyal74, Webbeh, larowlan, hudri, ryan.gibson, amietpatial, ddhuri, capysara, runeasgar, saranya ashokkumar, shimpy, nikitagupta: Editing menus user-experience has regressed

Issue #3111409 by mherchel, proeung, larowlan, alexpott, lauriii, Gábor Hojtsy, andrewmacpherson, catch, xjm, andypost, rahulrasgon, rabbitlair, mrconnerton, poojakural, boulaffasae, jerseycheese, shimpy, Indrajith KB, DuneBL, kiran.kadam911, komalkolekar, keboca, hawkeye.twolf, andrewozone, Maithri Shetty, alexdmccabe, sd9121, Sreenivas Bttv, katannshaw, mgifford, nod_, webchick, mtift, rainbreaw, Berdir, brianperry, thejimbirch, Dom., q0rban, nitesh624, hansa11, himanshu_sindhwani, kostyashupenko, shaktik, bnjmnm, sharma.amitt16, sonam.chaturvedi, steinmb, shaal, ressa, Ramya Balasubramanian, Sebacic, pradeepjha, tanmaykadam, thedrupalkid, vinitk, volkswagenchick, viappidu, vebrovski, Ujval Shah, Webbeh, Yuri, trebormc, msuthars, mrinalini9, bash247, chetanbharambe, ellenoise, anevins, andriyun, CocoM, JayKandari, ambuj_gupta, hussainweb, jhodgdon, Pooja Ganjage, ju.vanderw, jwitkowski79, MaxPah, Lokender Singh2, jponch, KarenS, KarinG, Lal_: Add new Olivero frontend theme to Drupal 9.1 core as beta; later make it stable and the default