Refactor formatting tooling and don't fire message when code cell is already formatted

[DavisVaughan]

Closes #932

The intent of the window.showInformationMessage("Editor selection is not within a code cell."); message seems to have mainly been about catching when Quarto: Format Cell was being called when you weren't actually in a code cell. I've done some refactoring to now fire this message when we fail to find a block at the user's cursor position, rather than later on when we fail to get edits for that block. It's perfectly legal for a formatter to return undefined as edits when there is nothing to do, and we shouldn't take that as a signal that we aren't in a code cell.

I've added a test for this specific case by mocking vscode.window.showInformationMessage() for the duration of the test so we can check that it gets called. Pretty neat way to test this.

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While I was working on this I felt the need to pay down some tech debt on how complicated these formatting functions have become. They are made up of extremely nested if statements and don't need to be (I've felt this pain every time I touch these functions). I think these are way easier to manage if you write them as a series of early exits.

Most of this PR is this refactor, but I don't expect it to change any actual behavior. I realize this is a bit messy though.

I think you should mostly approach this PR as a refactor, with a very minor change that I'll call out below.

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I test this with this qmd

```{python}
def fn():
  1+ 1
```

```{r}
1 + 1
```

```{r}
1 + 1
```


```{python}
def fn():
    1 + 1
```

[cscheid]

LGTM, and the flatter structure with early returns is so much cleaner to read, thank you.