Implement partial support for #define objects

[davispuh]

Consider common C pattern like:

struct S
{
  int a;
  int b;
};

#define S_INIT { 1, 2 }

int main()
{
   struct S s = S_INIT;
}

Currently dstep will ignore S_INIT which loses this "init" information.
This PR implements partial support so that

enum S_INIT = null; // FIXME: {1,2};

Will be produced, which allows to create simple shell script with simple sed command to afterwards fix up these case with something like this:

$ sed -iE 's|null; // FIXME: {\([^}]*\)}|S(\1)|g' file.d

Which will make final version to be:

enum S_INIT = S(1,2);

And that will work correctly when S_INIT is used.
Unfortunately this 2nd step with sed or another processing tool is needed because implementing usage-aware processing inside dstep is not trivial and would require significant effort to also parse macro usages so that's why I'm settling on this partial support.

[Copilot]

Pull request overview

Adds partial handling for object-like #define macros that expand to C braced initializer lists (e.g. {1,2}), so dstep can preserve that initializer information in generated D output (as a placeholder with a FIXME marker).

Changes:

• Extend the macro expression AST with a new braced-initializer expression node (ObjectExpr).
• Parse { ... } token sequences as a standalone expression in MacroParser.
• Translate this expression into a placeholder D value while retaining the original braced text in a FIXME comment.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
dstep/translator/TypeInference.d	Treats the new braced-initializer expression as Generic during type inference.
dstep/translator/MacroParser.d	Introduces ObjectExpr and parsing logic for { ... } object-style macro bodies.
dstep/translator/MacroDefinition.d	Adds translation support for ObjectExpr into a placeholder value with a FIXME marker.

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