builtin.jq: naive abs/0

manual.yml explains that the def is naive, and mentions fabs, etc.

tests/jq.test

@@ -1808,6 +1808,18 @@ false
 1
 1
 
+# abs, fabs, length
+abs
+"abc"
+"abc"
+
+map(abs)
+[-10, -1.1, -1e-1, 1000000000000000002]
+[10,1.1,0.1,1000000000000000002]
+
+map(fabs == length) | unique[0]
+[-10, -1.1, -1e-1, 1000000000000000002, -1000000000000000002]
+true
 
 # Using a keyword as variable/label name
 

tests/man.test

@@ -188,6 +188,10 @@ null
 1
 -1
 
+map(abs)
+[-10, -1.1, -1e-1, 1000000000000000002, -1000000000000000002]
+[10,1.1,1e-1,10000000000000002,1e+18]
+
 .[] | length
 [[1,2], "string", {"a":2}, null, -5]
 2