sql: improve LogicTest failure output for some cases
sql: improve LogicTest failure output for some cases

Turns something like:

    logic_test.go:701: testdata/explain_types:119: expected:
        "0"              "update"         "result"          "()"
        "1"              "select"         "result"          "(k"
        "int,"           "v"              "int,"            "\"k"
        "+"              "1\""            "int)"            "2"
        "render/filter"  "result"         "(k"              "int,"
        "v"              "int,"           "\"k"             "+"
        "1\""            "int)"           "2"               "render/filter"
        "render"         "0"              "(k)[int]"        "2"
        "render/filter"  "render"         "1"               "(v)[int]"
        "2"              "render/filter"  "render"          "2"
        "((k)[int]"      "+"              "(1)[int])[int]"  "3"
        "scan"           "result"         "(k"              "int,"
        "v"              "int)"           "3"               "scan"
        "filter"         "((v)[int]"      ">"               "(123)[int])[bool]"
        but found:
        "0"              "update"          "result"             "()"
        "1"              "select"          "result"             "(k"
        "int,"           "\"k"             "+"                  "1\""
        "int)"           "2"               "render/filter"      "result"
        "(k"             "int,"            "\"k"                "+"
        "1\""            "int)"            "2"                  "render/filter"
        "render"         "0"               "(k)[int]"           "2"
        "render/filter"  "render"          "1"                  "((k)[int]"
        "+"              "(1)[int])[int]"  "3"                  "scan"
        "result"         "(k"              "int,"               "v"
        "int)"           "3"               "scan"               "filter"
        "((v)[int]"      ">"               "(123)[int])[bool]"

Into:

    logic_test.go:701: testdata/explain_types:119:
        expected:
            0   update          result     ()
            1   select          result     (k int, "k + 1" int)
            2   render/filter   result     (k int, "k + 1" int)
            2   render/filter   render 0   (k)[int]
            2   render/filter   render 1   ((k)[int] + (1)[int])[int]
            3   scan            result     (k int, v int)
            3   scan            filter     ((v)[int] > (123)[int])[bool]

        but found:
            0  update         result    ()
            1  select         result    (k int, v int, "k + 1" int)
            2  render/filter  result    (k int, v int, "k + 1" int)
            2  render/filter  render 0  (k)[int]
            2  render/filter  render 1  (v)[int]
            2  render/filter  render 2  ((k)[int] + (1)[int])[int]
            3  scan           result    (k int, v int)
            3  scan           filter    ((v)[int] > (123)[int])[bool]

arjun4084346/cockroach,paperstreet/cockroach,paperstreet/cockroach,maxlang/cockroach,maxlang/cockroach,paperstreet/cockroach,veteranlu/cockroach,veteranlu/cockroach,vaibhavarora/cockroach,maxlang/cockroach,sunya123/cockroach,petermattis/cockroach,vivekmenezes/cockroach,vivekmenezes/cockroach,cockroachdb/cockroach,glycerine/cockroach,paperstreet/cockroach,vaibhavarora/cockroach,arjun4084346/cockroach,vaibhavarora/cockroach,arjun4084346/cockroach,cockroachdb/cockroach,cockroachdb/cockroach,vivekmenezes/cockroach,vaibhavarora/cockroach,maxlang/cockroach,sunya123/cockroach,arjun4084346/cockroach,petermattis/cockroach,glycerine/cockroach,vivekmenezes/cockroach,glycerine/cockroach,veteranlu/cockroach,petermattis/cockroach,maxlang/cockroach,arjun4084346/cockroach,petermattis/cockroach,cockroachdb/cockroach,vivekmenezes/cockroach,veteranlu/cockroach,glycerine/cockroach,glycerine/cockroach,cockroachdb/cockroach,maxlang/cockroach,sunya123/cockroach,sunya123/cockroach,veteranlu/cockroach,arjun4084346/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,petermattis/cockroach,sunya123/cockroach,paperstreet/cockroach,sunya123/cockroach,vaibhavarora/cockroach,vivekmenezes/cockroach,veteranlu/cockroach,cockroachdb/cockroach,sunya123/cockroach,arjun4084346/cockroach,maxlang/cockroach,paperstreet/cockroach,paperstreet/cockroach,maxlang/cockroach,petermattis/cockroach,vaibhavarora/cockroach,cockroachdb/cockroach,petermattis/cockroach,glycerine/cockroach,vivekmenezes/cockroach,petermattis/cockroach,glycerine/cockroach,vivekmenezes/cockroach,sunya123/cockroach,veteranlu/cockroach,veteranlu/cockroach,glycerine/cockroach,arjun4084346/cockroach,vaibhavarora/cockroach,paperstreet/cockroach