Add "short-index" version of often occurring ops about problem-solving

[lizmat]

If this works out, then maybe all 29 ops that have a string index, should get this treatment:

$ bceval c '.map({.name if .operands.first("str")}).unique.elems'                   
29

Which in the core setting would mean a saving of (2 * 228568) / 11983692 = 3.8% saving.

% bceval c '.grep(*.operands.first("str")).elems' 
228568