use explicit lambda-expression captures (bug #65318) Previously, we recommended using implicit capture by value (if possible) in all lambda expressions in Octave. However, this choice causes trouble in the transition period leading up to C++20, when the meaning changes for capturing 'this' by reference when the default capture is '='. Since all lambda expressions in Octave only need to capture a few variables it seems better and relatively easy to simply name all captured variable explicitly. (The maximum number of captured variables currently appears to be seven, including 'this', but the vast majority are capturing just one or two.) Affected files: Canvas.cc, GLCanvas.cc, QTerminal.cc, command-widget.cc, documentation.cc, files-dock-widget.cc, interpreter-qobject.cc, file-editor-tab.cc, file-editor.cc, octave-qscintilla.cc, main-window.cc, octave-dock-widget.cc, octave-qobject.cc, set-path-model.cc, settings-dialog.cc, variable-editor-model.cc, variable-editor.cc, call-stack.cc, gl2ps-print.cc, graphics.cc, input.cc, interpreter.cc, load-path.cc, mex.cc, pr-output.cc, strfns.cc, sysdep.cc, __delaunayn__.cc, audiodevinfo.cc, audioread.cc, oct-parse.yy, pt-eval.cc, Array-util.cc, Range.h, lo-sysdep.cc, lo-regexp.cc, oct-glob.cc, oct-string.cc, and url-transfer.cc.