[FEATURE] {flalign*} support for auto-newline, etc.

[eiiot]

Description of the Problem

When I'm using flalign* blocks, adding a newline simply adds the newline, rather than adding \\ and &.

Description of the Solution

I would love if a newline would trigger both \\ added to the previous line, and a & added to the beginning of the newline. As far as I'm aware, flalign* is the best way to do left-aligned multiline equations, so I tend to use them decently often.

Additional

My original plan was to create a snippet, but as far as I'm aware the newline functionality isn't a snippet but custom functionality within the plugin? I could be wrong here.

Here's the idea:

\begin{flalign*}
& \vec{v}_{i} = \vec{v}_{cm}=\vec{v}<CURSOR HERE>
\end{flalign*}

When pressing enter, becomes:

\begin{flalign*}
& \vec{v}_{i} = \vec{v}_{cm}=\vec{v}\\
& <CURSOR HERE>
\end{flalign*}