-Fix adding UTF-8 BOM to files

Steps to reproduce

Create a file with a fixable violation

Function Test-Function {
    param (
        [String]
        $Password
    )

    $Password
}

Run Invoke-ScriptAnalyzer -Path ./file.ps1 -Fix to fix the violation

Expected behavior

The violation is fixed but the BOM isn't added to the file. It should preserve whatever is there already.

Actual behavior

The violation is fixed but there is a UTF-8 BOM character added to the file

# Before
$ hexdump -C file.ps1

00000000  46 75 6e 63 74 69 6f 6e  20 54 65 73 74 2d 46 75  |Function Test-Fu|
00000010  6e 63 74 69 6f 6e 20 7b  0a 20 20 20 20 70 61 72  |nction {.    par|
00000020  61 6d 20 28 0a 20 20 20  20 20 20 20 20 5b 53 74  |am (.        [St|
00000030  72 69 6e 67 5d 0a 20 20  20 20 20 20 20 20 24 50  |ring].        $P|
00000040  61 73 73 77 6f 72 64 0a  20 20 20 20 29 0a 0a 20  |assword.    ).. |
00000050  20 20 20 24 50 61 73 73  77 6f 72 64 0a 7d 0a     |   $Password.}.|
0000005f

# After running -Fix
# hexdump -C file.ps1

00000000  ef bb bf 46 75 6e 63 74  69 6f 6e 20 54 65 73 74  |...Function Test|
00000010  2d 46 75 6e 63 74 69 6f  6e 20 7b 0a 20 20 20 20  |-Function {.    |
00000020  70 61 72 61 6d 20 28 0a  20 20 20 20 20 20 20 20  |param (.        |
00000030  5b 53 65 63 75 72 65 53  74 72 69 6e 67 5d 0a 20  |[SecureString]. |
00000040  20 20 20 20 20 20 20 24  50 61 73 73 77 6f 72 64  |       $Password|
00000050  0a 20 20 20 20 29 0a 0a  20 20 20 20 24 50 61 73  |.    )..    $Pas|
00000060  73 77 6f 72 64 0a 7d 0a                           |sword.}.|
00000068

Note the ef bb bf (UTF-8 BOM) present. I tried explicitly ignoring the rule UseBOMForUnicodeEncodedFile as well but the BOM is still added.

Environment data

> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      7.2.0
PSEdition                      Core
GitCommitId                    7.2.0
OS                             Linux 5.14.16-201.fc34.x86_64 #1 SMP Wed Nov 3 13:57:29 UTC 2021
Platform                       Unix
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

> (Get-Module -ListAvailable PSScriptAnalyzer).Version | ForEach-Object { $_.ToString() }

1.20.0

Start by reproducing the issue with Invoke-ScriptAnalyzer -Path ./file.ps1 -Fix on PowerShell 7.2 and inspect the file bytes before and after. Trace the -Fix path responsible for writing the file; done means the violation is fixed while the file's existing UTF-8 BOM state is preserved, including when UseBOMForUnicodeEncodedFile is ignored.