Drop-down list items are not XML escaped

[Arnie97]

Description

If any of the XML special characters <, >, &, " were used in SetDropList() choices, the produced file will be reported as corrupted.

Steps to reproduce the issue:

package main

import (
	"github.com/360EntSecGroup-Skylar/excelize/v2"
)

func main() {
	var jobs = []string{"R&D", "PM", "UX", "HR"}
	newWorkbookWithDropList(jobs)
}

func newWorkbookWithDropList(choices []string) {
	f := excelize.NewFile()
	dv := excelize.NewDataValidation(false)
	dv.Sqref = "A:A"
	if err := dv.SetDropList(choices); err != nil {
		panic(err)
	}
	f.AddDataValidation(f.GetSheetName(0), dv)
	f.SaveAs("TestDropList.xlsx")
}

Describe the results you received:

Describe the results you expected:

Output of go version:

go version go1.17rc1 linux/amd64

Excelize version or commit ID:

• master (e9ae9b4)
• v2.4.0 (d42834f)
• v2.1.0 (e51aff2)

Environment details (OS, Microsoft Excel™ version, etc.):

The following official implementation were tested, and all of them could reproduce this issue:

• Microsoft Office 365 for Mac, 16.49 (21050901)
• Microsoft Office 365 for Windows, 2102 (Build 13801.20808)
• Microsoft Office 2019 Professional Plus for Windows, 2105 (Build 14026.20302)
• Microsoft Office 2013 Professional Plus for Windows, 15.0.4919.1002

The following third-party implementations were also tested, but none of them was affected by the issue:

• Kingsoft WPS
• Apple Numbers
• Google Sheets
• LibreOffice

[xuri]

Thanks for your feedback, I have fixed it, please try to use the master branch code, and this patch will be released in the next version.