Sending DP shortcut code through NQ

[sloorush]

@cursork: In keypresshandler.js, we can add handlers from dyalog keycodes.

Double check ⎕WC behavior

[cursork]

Had a suspicion this already worked. Working demo:

 DemoDP connected;F

 F←'F1'
 F eWC'Form' 'DP Round-Trip (#444)'(50 50)(250 470)('Coord' 'Pixel')

 (F,'.E1')eWC'Edit' ''(20 20)(25 430)('Event' 'KeyPress' 'CBDPKey')
 (F,'.SEND')eWC'Button' 'Send DP'(60 20)(34 150)('Event' 'Select' 'CBDPSend')
 (F,'.STATUS')eWC'Label' 'Click "Send DP" to start the round-trip.'(120 20)(40 430)
 (F,'.COUNT')eWC'Label' 'Round-trips completed: 0'(175 20)(25 430)

 CBDPKey args

 :If 2<≢args
 :AndIf 'DP'≡3⊃args
     :If 0=⎕NC'DP_COUNT'
         DP_COUNT←0
     :EndIf
     DP_COUNT+←1
     'F1.STATUS'eWS'Caption' 'Got DP back from the client — round-trip complete ✓'
     'F1.COUNT'eWS'Caption'('Round-trips completed: ',⍕DP_COUNT)
     'F1.E1'eWS'Text'('DP #',⍕DP_COUNT)
 :EndIf

 CBDPSend args

 'F1.STATUS'eWS'Caption' 'Sent DP → waiting for the client to echo it back…'
 eNQ 'F1.E1' 'KeyPress' 'DP'