Improve elixir language

[Matsa59]

• Add f = pattern support for auto indent
• Improve multilines

Fix issue : #1188

[fxbois]

The patch is not ok
</form> is not a control block

[Matsa59]

@fxbois What do you mean by control block? I have no idea how I could add as a closing block element for an elixir block

Edit : I undertand what you said for </form> where can I add this rule ?
For the moment is not so bad, it just break the auto indent for the if we don't have the <form ..>. I mean it fix the auto indent that return to line automatically

[wkirschbaum]

How relevant would this be in the future, as the new .heex syntax would be <.form let={f} for={:search} phx-change="chg-search" phx-submit="sbt-search">...<.form> and .leex seems to be on the path of being deprecated. I speak under correction.

update:

yes, the above syntax will be deprecated and not thinking the extra complexity is worth adding as it has to cater for an unbalanced form tag.