Editor: Merge some minor bug fixes.
There were some tweaks made to the post editor in WordPress 5.0 that hadn't been merged to trunk, this commit rectifies that.
Merges [43815,43816] from the 5.0 branch to trunk.
Props birgire, jorbin, abdullahramzan, adamsilverstein, mrahmadawais, airathalitov, ajitbohra, schlessera, albertomedina, aldavigdis, alexsanford1, xyfi, nitrajka, afercia, andreiglingeanu, euthelup, aduth, sumobi, anevins, azaozz, androb, andrewserong, kallehauge, nosolosw, apeatling, atimmer, arnaudban, asvinballoo, b-07, benlk, blowery, caxco93, benjamin_zekavica, kau-boy, bernhard-reiter, bcolumbia, bph, boblinthorst, bradyvercher, bpayton, brentswisher, bronsonquick, burhandodhy, icaleb, chouby, ehg, chrisvanpatten, butimnoexpert, christophherr, chriskmnds, claudiosanches, danielbachhuber, mrmadhat, danielhw, danieltj, goldsounds, dfangstrom, daniloercoli, dannycooper, nerrad, dsawardekar, davemoran118, davidherrera, dryanpress, davidsword, davisshaver, dmsnell, dlocc, diegoreymendez, dd32, dency, ocean90, donnapep, chopinbach, electricfeet, eliorivero, sewmyheadon, ericnmurphy, foobar4u, circlecube, fabs_pim, flixos90, floriansimeth, gma992, garrett-eclipse, garyj, pento, doomwaxer, revgeorge, gziolo, bordoni, hardeepasrani, helen, luehrsen, herbmiller, toro_unit, ianbelanger, iandunn, igorsch, ipstenu, ireneyoast, israelshmueli, sisanu, jd55, copons, jnylen0, jamestryon, ephoxjames, jamiehalvorson, jsnajdr, jagnew, dciso, octalmage, vengisss, jhoffm34, shenkj, audrasjb, jblz, jeremyfelt, motleydev, jipmoors, sephsekla, joemaller, joemcgill, joen, johndyer, johnjamesjacoby, joshuawold, johnny5, desrosj, jonsurrell, belcherj, sirjonathan, koke, jorgefilipecosta, shelob9, jvisick77, julienmelissas, kopepasah, kadamwhite, codebykat, ryelle, gwwar, kevinwhoffman, coderkevin, ixkaito, kjellr, obenland, lancewillett, postphotos, loicblascos, lucasstark, luigipulcini, lucaskowalski, lukepettway, mahdiyazdani, mahmoudsaeed, mkaz, tyxla, markjaquith, mapk, vindl, m-e-h, mboynes, mattheu, lonelyvegan, mtias, napy84, maurobringolf, maximebj, mayukojpn, woodent, michaelhull, mmtr86, stubgo, simison, mihai2u, mike-haydon-swo, mnelson4, mpheasant, mikeschroder, idpokute, mikeyarce, dimadin, gonzomir, milesdelliott, warmarks, munirkamal, nfmohit, nateconley, greatislander, njpanderson, notnownikki, nielslange, nikschavan, potbot, nshki, webmandesign, oskosk, pglewis, pareshradadiya-1, swissspidy, pbearne, pauldechov, psealock, paulstonier, paulwilde, pedromendonca, ptasker, peterwilsoncc, tyrannous, strategio, piersb, delawski, prtksxna, presskopp, rachelbaker, rachelmcr, rakshans1, rahmon, lamosty, youknowriad, riddhiehta02, noisysocks, deviodigital, sanchothefat, robertsky, _dorsvenabili, rohittm, magicroundabout, rmccue, welcher, ryo511, sagarprajapati, samikeijonen, scottmweaver, kluny, sharaz, giventofly76, designsimply, sstoqnov, hypest, netweb, stevehenty, stuartfeldt, sergioestevao, soean, tammie_l, karmatosed, thrijith, timgardner, timmydcrawford, tjnowell, mirucon, travislopes, truongwp, tjfunke001, vishalkakadiya, vtrpldn, walterebert, westonruter, skorasaurus, somtijds, earnjam, williampatton, willybahuaud, yoavf, zebulan, ziyaddin, abhijitrakas, andreamiddleton, csabotta, dixitadusara, etoledom, faishal, hideokamoto, imath, iseulde, j-falk, jaswrks, johnwatkins0, jomurgel, notlaura, leahkoerper, mcsf, meetjey, 0mirka00, mitogh, ephoxmogran, tacrapo, mzorz, nagayama, omarreiss, ramonopoly, rileybrook, tinkerbelly, shaileesheth, sikander, ssousa, tfrommen, yahil.
Fixes #45037.