Improve performance of repeating strings (#3272)

This commit improves the performance of repeating strings, by copying
the result string instead of the string being repeated. Also it adds
an error message when the result string is too long.

tests/jq.test

@@ -1460,6 +1460,18 @@ indices("o")
 "abc"
 [null,null]
 
+. * 100000 | [.[:10],.[-10:]]
+"abc"
+["abcabcabca","cabcabcabc"]
+
+. * 1000000000
+""
+""
+
+try (. * 1000000000) catch .
+"abc"
+"Repeat string result too long"
+
 [.[] / ","]
 ["a, bc, def, ghij, jklmn, a,b, c,d, e,f", "a,b,c,d, e,f,g,h"]
 [["a"," bc"," def"," ghij"," jklmn"," a","b"," c","d"," e","f"],["a","b","c","d"," e","f","g","h"]]