patch 8.2.0864: pragmas are indented all the way to the left

Problem:    Pragmas are indented all the way to the left.
Solution:   Add an option to indent progmas like normal code. (Max Rumpf,
            closes #5468)

runtime/doc/indent.txt

@@ -570,9 +570,15 @@ The examples below assume a 'shiftwidth' of 4.
 	      with "#" does not work.
 
 
+	PN    When N is non-zero recognize C pragmas, and indent them like any
+	      other code; does not concern other preprocessor directives.
+	      When N is zero (default): don't recognize C pragmas, treating
+	      them like every other preprocessor directive.
+
+
 The defaults, spelled out in full, are:
 	cinoptions=>s,e0,n0,f0,{0,}0,^0,L-1,:s,=s,l0,b0,gs,hs,N0,E0,ps,ts,is,+s,
-			c3,C0,/0,(2s,us,U0,w0,W0,k0,m0,j0,J0,)20,*70,#0
+			c3,C0,/0,(2s,us,U0,w0,W0,k0,m0,j0,J0,)20,*70,#0,P0
 
 Vim puts a line in column 1 if:
 - It starts with '#' (preprocessor directives), if 'cinkeys' contains '#0'.