[Bug] Opening angle bracket not escaped in Markdown output

[alexeyzimarev]

Describe the bug
When using docfx metadata to generate Markdown output, most of the Markdown-supported characters are properly escaped with \. However, opening angle brackets aren't escaped, which causes some static site generators to fail as they expect an HTML tag when processing opening angle brackets.

To Reproduce
Use a config file similar to this, with outputFormat set to markdown:

{
    "metadata": [
        {
            "src": [{
                "files": ["*.dll"],
                "src": "./output"
              }],
            "dest": "docs/docs/api",
            "outputFormat": "markdown"
        }
    ]
}

Run docfx metadata. Inspect Markdown output.

Notice that opening angle brackets aren't escaped, whilst closing angle brackets are:

#### Implements

[IReadOnlyCollection<Parameter\>](https://learn.microsoft.com/dotnet/api/system.collections.generic.ireadonlycollection\-1), 
[IEnumerable<Parameter\>](https://learn.microsoft.com/dotnet/api/system.collections.generic.ienumerable\-1), 

Expected behavior

Output like this:

#### Implements

[IReadOnlyCollection\<Parameter\>](https://learn.microsoft.com/dotnet/api/system.collections.generic.ireadonlycollection\-1), 
[IEnumerable\<Parameter\>](https://learn.microsoft.com/dotnet/api/system.collections.generic.ienumerable\-1), 

Context:

• OS: macOS 14.5
• Docfx version: 2.76.0

[filzrev]

These appear to be the same issues reported in #9719.

However, opening angle brackets aren't escaped, which causes some static site generators to fail as they expect an HTML tag when processing opening angle brackets.

Currently markdown output format is intended to be used as input for docfx build command.
And following problems are known other than #9719 when markdown files are used by other tools.

• Raw <xref> tag is rendered to markdown files. ([Bug] .NET API / Markdown: Unresolved cref / xref tags from <summary> in generated markdown. #9879)
• Empty <a> tag for anchor at headings ([Feature Request] Make <a/> tag in headers optional when outputFormat: markdown #9720)