Unable to parse accessor function when using arrow functions with a block body

**I'm submitting a bug report**

* **Library Version:**
2.0.0

* **Operating System:**
Windows 10

* **Node Version:**
20.11.1

* **NPM Version:**
10.2.4

* **JSPM OR Webpack AND Version**
webpack 5.90.3

* **Browser:**
all

* **Language:**
TypeScript 5.4.2

**Current behavior:**
I'm using Webpack 5 with `new AureliaPlugin({dist: "es2015})` and typescript `target: "es6"`.
This config causes a runtime error when using arrow functions with a block body as accessor functions:

```
Inner Error:
Message: Unable to parse accessor function:
(model) => {
return model.name;
}
Inner Error Stack:
Error: Unable to parse accessor function:
(model) => {
return model.name;
}
at getAccessorExpression (webpack-internal:///aurelia-validation:569:15)
at PropertyAccessorParser.parse (webpack-internal:///aurelia-validation:552:30)
at FluentEnsure.ensure (webpack-internal:///aurelia-validation:1651:44)
at ValidationRules.ensure (webpack-internal:///aurelia-validation:1715:58)
```

Workaround: instead of using
```
// failing accessor function
.ensure((model) => {
return model.name;
})
```
it is possible to use the old fashioned style or the one-liner
```
// working accessor functions
.ensure(function(model) {
return model.name;
})

.ensure((model) => model.name)
```

**Expected/desired behavior:**

* **What is the expected behavior?**
Update arrow function regex to allow arrow functions with a function body. This could be handy to support automatically formatted code.
https://github.com/aurelia/validation/blob/f1628a3ccf3d526b98dadeda7ac9672f70c20e37/src/property-accessor-parser.ts#L33

Start with src/property-accessor-parser.ts at the linked line, where the accessor function is parsed. Reproduce the reported failure with a block-bodied arrow function and compare it with the working function and expression-bodied arrow examples. Done means block-bodied arrow accessors parse successfully without breaking the existing forms.

Written by the indexing model from the issue text.