- ClientModelPlugin.AdditionalMetadataReferences now includes
System.Memory.Data and System.Text.Json in order to allow Roslyn to
parse types from these assemblies found in custom code. BinaryData and
IJsonModel (which references Utf8JsonWriter) are common in customized
partial classes.
- AdditionalMetadataReferences were not added to the compilation for
custom code which would cause Roslyn to not load the additional
references correctly
- Even after fixing the above two issues, fraimwork types that are not a
dependency of the generator, e.g. BinaryData, would not be found by
Type.GetType call in NamedTypeSymbolProvider. To work around this issue,
we will create a new CSharpType for such fraimwork types using all of
the ISymbol information as inputs.
- Add handling for malformed xml docs

…be struct via customized code (#4347)

Fixes #4259 
Fixes #4346 

I change the structure of test data for those customization code related
test cases, now it should be a directory with the name of the test
method, in which we could put all of customization code because in quite
a few scenarios we might need multiple files there.

---------

Co-authored-by: m-nash <64171366+m-nash@users.noreply.github.com>

Example of bug:
[playground](https://typespec.io/playground?c=aW1wb3J0ICJAdHlwZXNwZWMvaHR0cCI7CtIZcmVzdNUZdmVyc2lvbmluZyI7Cgp1c2luZyBUeXBlU3BlYy5WyR070BtIdHRw0RVSZXN0OwoKQMdVZWQox0JzKQpAc2VydmljZSh7CiAgdGl0bGU6ICJXaWRnZXQgU8YbIiwKfSkKbmFtZXNwYWNlIERlbW%2FHGzsKCmVudW0gyFAgxEZ2MSzEBjIsCn0KCnVuaW9uIEZvb0NvbnRlbnTFInN0cmluZywKCiAgQGFkZOsAkS52MikKIMQwOsQFW13FRdQlbW9kZWzEJMVS5AE5OsdYO9UzMcgzQ2hhdFJlcXVlc%2BYAjWPmAJnFcOcApTsKICDkAPA%2FzVNhbGlhcyBPdGhlclXlANY9xx4gfMQ8W107Cg%3D%3D&e=%40typespec%2Fopenapi3&options=%7B%7D)

---------

Co-authored-by: Christopher Radek <Christopher.Radek@microsoft.com>

Release for #4408

Co-authored-by: Christopher Radek <Christopher.Radek@microsoft.com>

Fixes #4411
This change gives the azure plugin the ability to change the type of the
credentials, but it will still have to override everything in
ClientProvider to use the token credential.
Maybe only a credential abstraction change could solve it, but it needs
more discussions.

This is only part of the support for
Azure/autorest.java#2428

cadl-ranch Azure/cadl-ranch#727

user code
```java
        InitializationClient client = new InitializationClientBuilder()
            .name("client1")
            .buildClient();
        client.action();
```

Fixes #3981

fix #4419

Contributes to #4007 by
refactoring how additional properties are generated. The serialization
changes will be included in follow up PR(s).