Quite a few of these are already covered elsewhere in the rules. In the rest it would be up to the arbiter to use his judgement. I will quote the rules where relevant and state what I would have done as an arbiter.
2.1 Player A leaves the table (not the hall) - it is Player A's turn to move.
Explicitly covered by article 12.2:
Players are not allowed to leave the ‘playing venue’ without permission from the arbiter. The playing venue is defined as the playing area, rest rooms, refreshment area, area set aside for smoking and other places as designated by the arbiter.
The player having the move is not allowed to leave the playing area without permission of the arbiter.
So player A is free to leave the table, but not the playing area.
2.2 Player A stands behind Player B's chair on Player A's turn.
This type of behaviour is not explicitly covered outside of article 12.6, but unless player A was doing something unreasonably distracting like leaning over player B, I don't see a big problem with this, however if player B does make a complaint about being distracted by it I may ask Player A not to do so. It's at the arbiter's discretion.
2.3 Player A stands behind Player B on Player B's turn.
2.4 Player A plays without sitting down - it is player A's turn.
2.5 Player A is seated and fidgets continously.
These are all pretty similar and would be handled as for 2.2, it would be at the arbiter's discretion to decide what if any action to take about it.
2.6 Player A stares continually/makes faces at Player B.
This time the behaviour is clearly distracting and the arbiter should take action if the behaviour can be proven or was seen by the arbiter. If player B makes this complaint and I/other witnesses did not see player A doing anything wrong, I could not take any action directly, but would make sure to observe player A from then on to see if any such behavior takes place.
2.7 Player A does not write down the moves.
Explicitly covered by article 8.1:
8.1 In the course of play each player is required to record his own moves and those of his opponent in the correct manner, move after move, as clearly and legibily as possible, in the algebraic notation (See Appendix C), on the scoresheet prescribed for the competition.
It is forbidden to write the moves in advance, unless the player is claiming a draw according to Article 9.2, or 9.3 or adjourning a game according to the Guidelines of Adjourned Games point 1.a.
A player may reply to his opponent’s move before recording it, if he so wishes. He must record his previous move before making another.
Both players must record the offer of a draw on the scoresheet. (See Appendix C.13)
If a player is unable to keep score, an assistant, who must be acceptable to the arbiter, may be provided by the player to write the moves. His clock shall be adjusted by the arbiter in an equitable way.
So both players are required to write down the moves anyway.
2.8 Player A's mobile phone is switched off but its alarm rings. Will Player A be forfeited?
Explicitly covered in article 12.3:
Without the permission of the arbiter a player is forbidden to have a mobile phone or other electronic means of communication in the playing venue, unless they are completely switched off. If any such device produces a sound, the player shall lose the game. The opponent shall win. However, if the opponent cannot win the game by any series of legal moves, his score shall be a draw. ...
So yes, player A would be forfeited. The rules state only that the device needs to make any kind of sound for the player to be forfeited.