(ON HOLD) [Feature request] Replace "else if" with "elif"

Test1:
```fsharp
if foo then
    ()
else if bar then
    ()
```
should become:
```fsharp
if foo then
    ()
elif bar then
    ()
```

---

Test2:
```fsharp
if foo then
    ()
else
    if bar then
        ()
    else
        ()
```
should become (same):
```fsharp
if foo then
    ()
else
    if bar then
        ()
    else
        ()
```
(should not change)