Rename the 'Text' tab of the classic editor to 'Code', mimicking the labels used in the block editor: "Visual editor" and "Code editor".
Update code comment and Help documentation to reference the editor using the new label.
Props lukecavanagh, ctienshi, travel_girl, audrasjb, sabernhardt, joedolson, rseigel, mark-k, sergeybiryukov, presskopp, giuriani, afercia, knutsp, audrasjb, sukhendu2002.
Fixes#38061.
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git-svn-id: http://core.svn.wordpress.org/trunk@59038 1a063a9b-81f0-0310-95a4-ce76da25c4cd