[Version 14.0] Support optional and named arguments in Expression trees

V14 has an [MS Proposal](https://github.com/dotnet/csharplang/blob/main/proposals/csharp-14.0/optional-and-named-parameters-in-expression-trees.md) for the feature "Support optional and named arguments in Expression trees." It proposes we remove certain restrictions. However, I cannot find any text in the standard that prohibits these things.

Start with the linked C# 14 proposal on optional and named arguments in expression trees, then search the csharpstandard repository for the current expression-tree restrictions. Compare the proposal with the relevant standard text and identify whether a wording change is needed to reflect the intended support.

Written by the indexing model from the issue text.