feat: Add feature to configure markdig extension by docfx.json configs.

[filzrev]

This PR supersede #9780.

This PR intended to add functionality to override settings for some specific Markdig extensions.

Changed behaviors

1. When markdig extension name ONLY specified.
   -> Then try to add or replace extension with markdig default options. (Used to reset docfx default settings)
2. When markdig extension name with options are specified.
   -> Then try to add or replace extension with specified options.

Other markdig extensions that have not customizable configs are processed same as before..
(By using MarkdownPipelineBuilder.Configure method ).

---

What's changed in this PR

1. Add MarkdigExtensionSetting.cs file.

• This class represent extension name with custom options.
• options are hold with System.Text.JsonElement

2. Add MarkdigExtensionSettingConverter.cs file.

• This class convert json config to MarkdigExtensionSetting object.

3. Modify MarkdownExtensions.cs logics.

• If known extension names are passed. It try to add or replace markdig extension with specified options.

4. Modify MarkdownServiceParameters.cs

• MarkdigExtensions propety type is changed from string[] to MarkdigExtensionSetting.

5. Update public API contracts file (Api.verified.cs)
6. Add unit tests for markdig extension that can specify custom option settings.

Additional Notes
Original reported feature requests (#9762 / #9772) are resolved by this PR.
By using following configurations.

{
  "build": {
    "markdownEngineProperties": {
      "markdigExtensions": [
        "EmphasisExtras",
        "Emojis"
      ]
    }
  }
}

If it need to specify options.
Pass options properies with extension name.

markdigExtensions: [
    "FootNotes",
    { "Emojis": { "options": {  "enableSmileys": true } },
    { "AutoIdentifiers": { "options": "default" } },
    { "MediaLinks": { "options": { "width": 800, "height": 400 }} 
]

[codecov]

Codecov Report

Attention: Patch coverage is 60.86957% with 45 lines in your changes are missing coverage. Please review.

Project coverage is 78.95%. Comparing base (fe673ec) to head (f25547f).
Report is 98 commits behind head on main.

Files	Patch %	Lines
...ine.Extensions/MarkdigExtensionSettingConverter.cs	28.57%	30 Missing ⚠️
...arkdigEngine.Extensions/MarkdigExtensionSetting.cs	64.70%	10 Missing and 2 partials ⚠️
...cfx.MarkdigEngine.Extensions/MarkdownExtensions.cs	92.10%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9820      +/-   ##
==========================================
+ Coverage   74.31%   78.95%   +4.63%     
==========================================
  Files         536      538       +2     
  Lines       23189    23311     +122     
  Branches     4056     4049       -7     
==========================================
+ Hits        17234    18406    +1172     
+ Misses       4853     3780    -1073     
- Partials     1102     1125      +23     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[yufeih]

Thank you @filzrev !