Linebreaks after 'get' or 'set' in class bodies are not parsed correctly (T7533)

> Issue originally made by @bakkot (as T7533 and later babel/babel#4432)
### Input code

```
class A {
  get
    x(){}
}
```
### Description

This code gives a parse error without the class-properties-transform plugin, and is parsed as a class containing a single method `x` with it. Neither is correct; it's valid syntax for a class with a getter (not method) for 'x'.
