Replace "Extended ASCII" with the specific encoding name

From the [Extended ASCII Wikipedia page](https://en.wikipedia.org/wiki/Extended_ASCII#Multi-byte_character_encodings)

> Using the term "extended ASCII" on its own is sometimes criticized,[1][2][3] because it can be mistakenly interpreted to mean that the ASCII standard has been updated to include more than 128 characters or that the term **unambiguously identifies a single encoding**, neither of which is the case.

Emphasis mine. Knowing which extended ASCII encoding is being used in the password generator will allow users to find how many characters are in that encoding. This will allow users to manually calculate the bits of entropy for a given generated password.

Start by locating the password generator's encoding label and any related tests; the issue does not name a file or entry point. Determine the concrete encoding used, replace the ambiguous "Extended ASCII" wording with its specific name, and verify that users can use it to calculate the character count and entropy.

Written by the indexing model from the issue text.