Proposal: Use <( )> to embed code blocks in XML literals, string literals, and in any expression

I suggest to embed VB code blocks in xml literals like this
```VB.NET
Dim x =

I think the `<( )>` is a suitable quote. The <%= %> will continue used to embed values. The `<( )>` will grantee not to break any existing code. It is supposed to return a value, so it is lowered to a function call:

```VB.NET
Dim x =

Notes:
1. If there is an XElement or a string literal in a separate line inside `<( )>`, implicit return is assumed.
2. If there is an XElement or a string literal inside a loop, implicit Yield is assumed
3. If there is nothing to return or yield in the block, `Return Nothing` is assumed. This will allow writing Subs also to define some variables in the XML literal scope.
4. We can use same Razor `@` rules to switch between text, VB Code, and XML Literals. Again, since the `<( )>` is new quote, there is no fear to break any existing code.

Note that This proposal can be implemented using @AnthonyDGreen 's [Top-Level Code Prototype]( https://anthonydgreen.net/2019/04/23/top-level-code-scenario-a/) can achieve this proposal:
```vb.net
Dim timeOfWeek = <( Select Case Date.Today.DayOfWeek
Case DayOfWeek.Monday To DayOfWeek.Friday
"Work Week"
Case DayOfWeek.Saturday, DayOfWeek.Sunday
"Weekend"
End Select )>
```

and many more, like embedding code in interpolated strings
```vb.net
Dim Msg= $" time Of Week is {<( Select Case Date.Today.DayOfWeek
Case DayOfWeek.Monday To DayOfWeek.Friday
"Work Week"
Case DayOfWeek.Saturday, DayOfWeek.Sunday
"Weekend"
End Select )>}"
```