Llvmir2hll: prevent invalid substitutions in CopyPropagation

Modify `CopyPropagation` (or other analyses) to not perform invalid substitutions. E.g.:
```c
"abcd"[2] = 4;
```
```c
int32_t v12 = *NULL;
```
Invalid substitutions (where `CONST` is constant/literal):
```
CONST()
CONST[index]
CONST.index (zahrnuje CONST->index)
*CONST
&CONST
```

Locate the CopyPropagation analysis and inspect how it handles the listed constant expressions and dereferences. Reproduce the examples, then verify that invalid substitutions such as CONST(), CONST[index], CONST.index, *CONST, and &CONST are no longer performed.

Written by the indexing model from the issue text.