Add "Show Encryption Key" toggle

[gtibo]

What
I changed the behavior of the Encryption Key LineEdit

1. By default, secrets should be hidden, and only displayed if requested by user.

2. A toggle option to display the Encryption Key of the project export windows.

3. The key becomes hidden again when Encrypt Export is deactivated (reactivating it does not reactivate the “show key” toggle).

Why?

• As a general rule, “secret” strings should not be readable by default.
• Avoid key leaking by mistake (e.g. visible on screenshots, displayed by mistake, etc.)

[KoBeWi]

The code needs some work, but overall seems fine.

Could use a review from someone more familiar with encryption.

[bruvzg]

It would be better to do it as a toggle button after the line edit, instead of a full option on its own line. Similar style to #104742.

[gtibo]

It would be better to do it as a toggle button after the line edit, instead of a full option on its own line. Similar style to #104742.

Done :)

[Calinou]

Tested locally, it works as expected. Code looks good to me.

[llama-nl]

@gtibo could you also do this for release and debug password in Android Export or @syntaxerror247 can do something

[Repiteo]

Thanks!