Co-authored-by: Valentin Touzeau <tree-sitter.github@valentintouzeau.fr>

This commit merges functions "elseBlock" and "elifBlock" in a single
function "alternativeBlock". Any call to either function is replaced by
a call to "alternativeBlock", which cover all alternatives (elif,
elifdef and else). The goal is twofold:

1) Correct the grammar to allow all kind of alternatives independently
   of the "if" directive. Before the fix, "#if" alternative was
   generated by elseBlock only, and thus disallow "#elifdef" as a
   follow-up.
2) As a side effect, simplify the parser.

Specifically for Neovim which contains code like:

```c
Dictionary nvim_eval_statusline(String str, Dict(eval_statusline) *opts, Arena *arena, Error *err)
  FUNC_API_SINCE(8) FUNC_API_FAST
{
  ...
}
```

Now allows `<string> <identifier> ...` forms of concatenations.

Co-authored-by: Denny Sun <dennys@microsoft.com>

We do ensure at least one string is present though, otherwise conflicts arise

This fixes a slight regression when parsing a preproc function definition using division operators

`a *= b != c ? d : e;` is parsed incorrectly as a result

This reverts commit eb6649e0c2.

Previously, pointers were associated with the function identifier, now they're associated with the return type

This resolves conflicts with declarations that can be interpreted as binary_expressions