debug: 'value' of Variables response for a large struct is incomprehensible

[hyangah]

dlv-dap: built at master (7d343b6) on Apr 18, 2021.
vscode-go: 0.24.1

How to reproduce:

Evaluate a variable of a complex struct type.

dlv cli output is also long, but it is presented as a multi-line string, so that is not too bad.

If the context is 'repl', maybe present it as a multi-line string.
If the context is 'variables', maybe we don't need such a long string in some clients (e.g. vscode)

[hyangah]

PR go-delve/delve#2513 that truncates the string representation of compound type if it's longer than 256 and it's not for clipboard or hover mode has been merged. So, closing this.

We will keep polishing the value representation further so the representation is compact while useful information is still easily accessible.