Stack structure detection without leveraging type information

Consider the following C code:

#include <stdio.h>

struct foobar
{
    int a;
    int b;
    int c;
};

int func(struct foobar* f)
{
    return f->a + f->b + f->c;
}

int main()
{
    struct foobar f;
    f.a = 123;
    f.b = 456;
    f.c = 789;
    int result = func(&f);
    printf("result: %d\n", result);
}

The default decompilation looks like this:

Since the analysis does not see the var_1c, var_18, and var_14 all belong to a structure, it marks the latter two as dead store. While the result is reasonable, it would be great if we can actually detect the case and create the stack structure.

Note this is different from https://github.com/Vector35/binaryninja-api/issues/773, when we already know the type of the _func function -- that is just a type propagation. This issue suggests the capacity to detect the structure even if the function type is not set

Reproduce the supplied C example and inspect where var_1c, var_18, and var_14 are treated as separate stack variables. Compare the behavior with issue #773, which covers propagation when the function type is already known. Done means the decompiler can recognize the shared stack structure without a preset function type.