Replace bytes.NewReader(stringToBytes(s)) with strings.NewReader(s)

[dolmen]

Description

Drop unnecessary uses of internal function stringToBytes.

Motivation and Context

stringToBytes uses package unsafe. stringToBytes is just a speed hack that kills portability. stringToBytes doesn't have a benchmark ensuring it helps for spped

This also reduces allocations as shown by benchmarks results.

How Has This Been Tested

go test
go test -bench B  -benchmem   # BenchmarkSetCellValue still fails like before my change

Benchmark before (66d0272):

goos: darwin
goarch: amd64
pkg: github.com/360EntSecGroup-Skylar/excelize/v2
BenchmarkOpenFile-4              	     566	   2753542 ns/op	  534112 B/op	    4476 allocs/op
BenchmarkWrite-4                 	       2	 630348442 ns/op	122600148 B/op	 1833689 allocs/op
BenchmarkAddPictureFromBytes-4   	   10000	    583967 ns/op	    6939 B/op	      38 allocs/op
BenchmarkRows-4                  	    2625	    477113 ns/op	  103223 B/op	    2304 allocs/op
BenchmarkStreamWriter-4          	    1809	    565083 ns/op	  133545 B/op	    4464 allocs/op

Benchmark after:

goos: darwin
goarch: amd64
pkg: github.com/360EntSecGroup-Skylar/excelize/v2
BenchmarkOpenFile-4              	     631	   1977463 ns/op	  533661 B/op	    4475 allocs/op
BenchmarkWrite-4                 	       2	 628304756 ns/op	122599896 B/op	 1833686 allocs/op
BenchmarkAddPictureFromBytes-4   	   10000	    562723 ns/op	    6939 B/op	      38 allocs/op
BenchmarkRows-4                  	    2395	    442256 ns/op	  103245 B/op	    2305 allocs/op
BenchmarkStreamWriter-4          	    1896	    731839 ns/op	  133538 B/op	    4463 allocs/op

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[xuri]

LGTM, thank you.