Add diagnostics for semicolon at the end of function

This change introduce diagnostics when there is a semicolon at
the end of the function body:
```cpp
g: () = {};
```
Generates:
```
error: a compound function body shall not end with a semicolon (at ';')
```
And
```cpp
g: () = 42;;
```
Generates:
```
error: a short function syntax shall end with a single semicolon (at ';')
```

Author: filipsajdak

source/parse.h

@@ -5313,6 +5313,21 @@ class parser
             return {};
         }
 
+        if (
+            n->is_function()
+            && n->initializer
+            && !done() && curr().type() == lexeme::Semicolon
+            )
+        {
+            if (n->initializer->is_compound() && n->has_name()) {
+                error("a compound function body shall not end with a semicolon");
+                return {};
+            } else if (n->initializer->is_expression()) {
+                error("a short function syntax shall end with a single semicolon");
+                return {};
+            }
+        }
+
         //  If this is an implicit constructor, it must have two parameters
         if (n->is_constructor())
         {