chore: Change output html file encoding to UTF-8 (No BOM)

[filzrev]

What's included in this PR

• Change output HTML encoding from UTF-8(BOM) to UTF-8 (No BOM).

Background
Currently docfx output HTML files using UTF-8 (with BOM) encoding.
And other non-HTML files are using UTF-8 (No BOM).

Currently docfx output HTML with following meta tag. so it seems BOM is not required.

If there is any reason to use UTF-8(BOM) close this PR.
(For example. Snapshot tests library requires BOM)

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (277aa86) 77.58% compared to head (652594f) 77.58%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9131   +/-   ##
=======================================
  Coverage   77.58%   77.58%           
=======================================
  Files         591      591           
  Lines       24567    24568    +1     
=======================================
+ Hits        19060    19061    +1     
  Misses       5507     5507           

Files Changed	Coverage Δ
...x.Build.Engine/PostProcessors/HtmlPostProcessor.cs	90.24% <100.00%> (+0.24%)	⬆️

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[KalleOlaviNiemitalo]

Currently docfx output HTML with following meta tag. so it seems BOM is not required.

What's the meta tag? I don't see it in the description.

[filzrev]

What's the meta tag? I don't see it in the description.

Sorry it indicate <meta charset="utf-8"> (It's contains HTML tags so it's not rendered when using quote syntax)

default template
https://github.com/dotnet/docfx/blob/main/templates/default/partials/head.tmpl.partial#L4

modern template
https://github.com/dotnet/docfx/blob/main/templates/modern/layout/_master.tmpl#L9

[yufeih]

Looks great!