Chemical element NAMES from Specutils' "find_lines_threshold" method

Hello
I was wondering whether one could get the chemical element names (atoms, molecules, both neutral and/or ionized) from the methods **find_lines_threshold** and/or **find_lines_derivative**.
e.g.
```
lines = find_lines_threshold(spec1d_sub, noise_factor=2.5)
lines
```
One gets a QTable as shown below and I can identify some elements behind the identified lines.

Many thanks in advance

Start by reading the find_lines_threshold and find_lines_derivative entry points and reproduce the QTable output described in the issue. Determine whether chemical-element identification for neutral or ionized atoms and molecules is in scope, then define and document the expected result and validation before implementation.

Written by the indexing model from the issue text.