sqltemplate, dbimpl: Remove single-method function types (#107525)

* Remove dbProviderFunc function.

This removes one extra indirection that made the code bit more difficult to navigate.

* Remove indirection function types implementing single-method interfaces.

This streamlines the code and makes it bit easier to navigate.

* Update pkg/storage/unified/sql/sqltemplate/dialect_mysql.go

Co-authored-by: Mustafa Sencer Özcan <32759850+mustafasencer@users.noreply.github.com>

---------

Co-authored-by: Mustafa Sencer Özcan <32759850+mustafasencer@users.noreply.github.com>

pkg/storage/unified/sql/sqltemplate/dialect_postgresql.go

@@ -2,28 +2,29 @@ package sqltemplate
 
 import (
 	"errors"
+	"fmt"
 	"strings"
 )
 
 // PostgreSQL is an implementation of Dialect for the PostgreSQL DMBS.
-var PostgreSQL = postgresql{
-	rowLockingClauseMap: rowLockingClauseAll,
-	argPlaceholderFunc:  argFmtPositional,
-	name:                "postgres",
-}
+var PostgreSQL = postgresql{}
 
-var _ Dialect = PostgreSQL
-
-// PostgreSQL-specific errors.
 var (
 	ErrPostgreSQLUnsupportedIdent = errors.New("identifiers in PostgreSQL cannot contain the character with code zero")
 )
 
-type postgresql struct {
-	standardIdent
-	rowLockingClauseMap
-	argPlaceholderFunc
-	name
+type postgresql struct{}
+
+func (p postgresql) DialectName() string {
+	return "postgres"
+}
+
+func (p postgresql) ArgPlaceholder(argNum int) string {
+	return fmt.Sprintf("$%d", argNum)
+}
+
+func (p postgresql) SelectFor(s ...string) (string, error) {
+	return rowLockingClauseAll.SelectFor(s...)
 }
 
 func (p postgresql) Ident(s string) (string, error) {
@@ -33,7 +34,7 @@ func (p postgresql) Ident(s string) (string, error) {
 		return "", ErrPostgreSQLUnsupportedIdent
 	}
 
-	return p.standardIdent.Ident(s)
+	return standardIdent(s)
 }
 
 func (postgresql) CurrentEpoch() string {