dlv send to channel value similar to set variable.

Please answer the following before submitting your issue:

Note: Please include any substantial examples (debug session output,
stacktraces, etc) as linked gists.

1. What version of Delve are you using (`dlv version`)?
```
dlv version
Delve Debugger
Version: 1.4.0
Build: b09aed17fd986f81eba76a50e374fb3c5f8a491d
```
2. What version of Go are you using? (`go version`)?
```
go version
go version go1.14.5 darwin/amd64
```
3. What operating system and processor architecture are you using?
4. What did you do?
```
(dlv) n
> main.main() ./main_ch.go:6 (PC: 0x105e8f4)
1: package main
2:
3:
4: func main() {
5: ch := make(chan int, 4)
=> 6: ch <- 1
7: ch <- 2
8: ch <- 3
9: ch <- 4
10: close(ch)
11: }
(dlv) set ch <- 1
Command failed: 1:4: expected 'EOF', found '<-'
```
5. What did you expect to see?
something similar to `set` but for variables.

6. What did you see instead?

Reproduce the reported session with Delve 1.4.0 and the shown `set ch <- 1` command. Start by tracing the existing `set` command and determine how a channel-send operation should be accepted; done means the debugger supports sending a value to a channel similarly to setting a variable.

Written by the indexing model from the issue text.