cgosqlite: support named parameters with $ prefix

This allows using the "$VVV" syntax for named parameters in SQLite, as
described in https://sqlite.org/c3ref/bind_blob.html

Updates tailscale/corp#35883

Signed-off-by: Andrew Dunham <andrew@tailscale.com>

Author: andrew-d

cgosqlite/cgosqlite.go

@@ -357,6 +357,9 @@ func (stmt *Stmt) BindParameterIndexSearch(name string) int {
 	if i := stmt.BindParameterIndex("@" + name); i > 0 {
 		return i
 	}
+	if i := stmt.BindParameterIndex("$" + name); i > 0 {
+		return i
+	}
 	return stmt.BindParameterIndex("?" + name)
 }