Get all extension methods for type by use roslyn api
<p>I want get all extensions methods for type. For example for type <code>string</code> if I am use semanticmodel method lookupsymbols.</p>

<pre><code>var sourceText = @"string a = "";
a."
var tree= CSharpSyntaxTree.ParseText(sourceTextx...);
....
var members = semanticModel.LookupSymbols(source.IndexOf("a."), someType, includeReducedExtensionMethods: true);
//this return all members with extension methods for type string someExtMethod(this string text)....


//I want get all extension with methods where first param might be one of them 
var interfaces = someType.AllInerfaces;
//for example IEnumerable&lt;out T&gt;, methods like: Select, Where, Aggregate...
</code></pre>