Respect VIRTUAL_ENV_DISABLE_PROMPT in nushell activation script

[m-lima]

The activate.nu script was not respecting the VIRTUAL_ENV_DISABLE_PROMPT like other scripts. This PR addresses that.

The changes can be summarized as:

• Only add the prompt-related env vars if $env.VIRTUAL_ENV_DISABLE_PROMPT evaluates to false
• Like with other activation scripts, it will evaluate to false if the env var is missing, it is empty, it is '0'. Also, because of nushell type system and the use of the into bool built-in, anything that nushell can covert into a false will also work, e.g. the strings false and 0000 or 0.0.

There are no changes to the documentation since this is already an expected behavior.
Also, I did not add an entry to the changelog as the developer documentation states that "non trivial" changes should be added. I considered this change trivial, but please let me know if an entry is required.

Fixes: #2461

[gaborbernat]

This change is 52 new lines, and 28 removals, this is not trivial so let's add the changelog.

[m-lima]

This change is 52 new lines, and 28 removals, this is not trivial so let's add the changelog.

Sure, no problem. I'll create an issue then, so that I can reference the changelog (and fix the test)

By the way, that amount of changes is the indentation.. In reality is was more like 20 additions, that's why I made my initial judgement of triviality

[m-lima]

Interesting error. Looks like libc was not found to execute nushell? Or maybe nushell requires a specific version of glibc that is not present in the ubuntu vms running the test?
Or am I reading this wrong?