Query builder (#10104)

* add query builder to facilitate dynamic SQL construction

* leverage query builder to refactor user store

This is partially setup work for MM-13120, but merged to master to avoid
further conflicts.

* fix unrelated unit test breakage

* documentation tweaks

* Apply suggestions from code review

Co-Authored-By: lieut-data <jesse.hallam@gmail.com>

* prefer comma separated case options to fallthrough

* vendor github.com/Masterminds/squirrel and deps

* switch to using github.com/Masterminds/squirrel

* rm querybuilder

vendor/github.com/Masterminds/squirrel/part.go

@@ -0,0 +1,55 @@
+package squirrel
+
+import (
+	"fmt"
+	"io"
+)
+
+type part struct {
+	pred interface{}
+	args []interface{}
+}
+
+func newPart(pred interface{}, args ...interface{}) Sqlizer {
+	return &part{pred, args}
+}
+
+func (p part) ToSql() (sql string, args []interface{}, err error) {
+	switch pred := p.pred.(type) {
+	case nil:
+		// no-op
+	case Sqlizer:
+		sql, args, err = pred.ToSql()
+	case string:
+		sql = pred
+		args = p.args
+	default:
+		err = fmt.Errorf("expected string or Sqlizer, not %T", pred)
+	}
+	return
+}
+
+func appendToSql(parts []Sqlizer, w io.Writer, sep string, args []interface{}) ([]interface{}, error) {
+	for i, p := range parts {
+		partSql, partArgs, err := p.ToSql()
+		if err != nil {
+			return nil, err
+		} else if len(partSql) == 0 {
+			continue
+		}
+
+		if i > 0 {
+			_, err := io.WriteString(w, sep)
+			if err != nil {
+				return nil, err
+			}
+		}
+
+		_, err = io.WriteString(w, partSql)
+		if err != nil {
+			return nil, err
+		}
+		args = append(args, partArgs...)
+	}
+	return args, nil
+}