First, rename mLastRenderBottom to mLastRenderedOffset. The old name is
misleading because it actually holds the line that was at the top of the
screen when it was last rendered, not the bottom.

Also add explanation of what mScrollVector means.

These changes help understand the logic at TTextEdit::drawForeground().

TConsole is best viewer as a container of other widgets, rather than a
widget itself. Therefore, it makes more sense to add accessibility support
to its inner widgets.

…ibleTextEdit

Thanks to Stephen Lyons for the suggestion.

Use plain strings rather than QStringLiterals. The QStringLiteral()
versions add annoying double quotes to the output.

Also, use function calls rather than streams to output the messages. The
syntax is more compact and allows for better control of the formatting.

… interface_cast()

QAccessibleWidget's version already does that for us.

Also take the opportunity to remove some unnecessary headers.

Rely on the superclass' implementation.

It's redundant, because QAccessibleWidget's constructor already takes a
role argument.

This communicates that they're internal helpers for the class implementation and
aren't used anywhere else.

…contents

... as oposed to assuming that every (x, y) coordinate contains a character.

The current cursor position isn't relevant in the calculation.

This fixes the following warning:

  'TAccessibleTextEdit::text' hides overloaded virtual function

Adjust lineForOffset() and cursorPosition() to take into account the
newlines added by join().

Also, simplify text(int startOffset, int endOffset) using the new
text(QAccessible::Text t) method.

… on the last char

Support only selection 0.

…and textAtOffset()

It's partially based on QAccessibleTextWidget::attributes() from Qt 5.15.

Also, remove ‘DocumentContentChanged’ event from TConsole::print() methods
because both call TTextEdit::showNewLines(), which already sends
‘TextInsertEvent’.