[4.2] [BUG?] Added support for nested ternary statement in BladeCompiler.

As suggested by @GrahamCampbell in #4431, this pull request is now made to the 4.2 branch because the BladeCompiler has been updated.

There are occasions where nested ternary statements are useful. Before this commit, the following line did not produce expected results:

```
{{ $foo or ($bar or 'foobar') }}
```

Which would have been compiled to:

```php
<?php echo isset($foo) ? $foo : ($bar or 'foobar'); ?>
```

This PR fixed the problem and the BladeCompiler now parses the nested statement and compiled it to:

```php
<?php echo isset($foo) ? $foo : (isset($bar) ? $bar : 'foobar'); ?>
```