[GR-60209] Implement new foreign configuration file syntax.

[graalvmbot]

Implements a new, more user-friendly FFM API configuration file syntax.
Before this change, the configuration file syntax was based on the reverse-engineered toString representation of the function descriptors and memory layouts which turned out to be very tricky to use.

We therefore decided to introduce a syntax that aligns with the MemoryLayout factory methods.
The configuration file is still a JSON file. We now use a more JSON-style way to define a function descriptor:

{
  "downcalls": [
    { "returnType": "Layout", "parameterTypes": ["Layout", "Layout"] },
  ]
}

The syntax for a single returnType or parameterType is:

 Layout ::= Alignment | StructLayout | UnionLayout | SequenceLayout | ValueLayout | PaddingLayout
 Alignment ::= 'align' '(' Int ',' Layout ')'
 StructLayout ::= 'struct' '(' Layout* ')'
 UnionLayout ::=  'union' '(' Layout* ')'
 SequenceLayout ::= 'sequence' '(' Int ',' Layout ')'
 ValueLayout ::=  canonical layout (e.g. 'int', 'long', ...)
 PaddingLayout ::= 'padding' '(' Int ')'
 Int ::= a positive decimal integer

Example:

{ 
    "returnType":  "double", 
    "parameterTypes": ["sequence(10, long)", "struct(long, padding(8), long)", "union(int, double)"] 
}

Furthermore, for direct upcalls it is now possible to skip declaration of returnType and parameterTypes if the Java signature can be represented as FunctionDescriptor without ambiguity. This is the case if the Java signature does not contain any MemorySegment parameter or return type. For example:

Java:

public class MyClass {
    public static int foo(long x) {
        // ...
    }
    
    public static int foo(double x) {
        // ...
    }
}

Configuration File:

{
  "directUpcalls": [
    { "class", "MyClass", "method": "foo" },
  ]
}

This will register both overloads of MyClass.foo for direct upcalls.

An appropriate update of the docs (i.e. ForeignInterface.md) will follow in a separate PR.