Multiple vulnerabilities resulting in out-of-bounds writesCVE-2022-36086

* The heap initialization methods were missing a minimum size check for the given heap size argument. This could lead to **out-of-bound writes** when a heap was initialized with a size smaller than `3 * size_of::<usize>` because of metadata write operations. * When calling `Heap::extend` with a size smaller than two `usize`s (e.g., 16 on `x86_64`), the size was erroneously rounded up to the minimum size, which could result in an **out-of-bounds write**. * Calling `Heap::extend` on an empty heap tried to construct a heap starting at address 0, which is also an **out-of-bounds write**. * One specific way to trigger this accidentally is to call `Heap::new` (or a similar constructor) with a heap size that is smaller than two `usize`s. This was treated as an empty heap as well. * Calling `Heap::extend` on a heap whose size is not a multiple of the size of two `usize`s resulted in unaligned writes. It also left the heap in an unexpected state, which might lead to subsequent issues. We did not find a way to exploit this undefined behavior yet (apart from DoS on platforms that fault on unaligned writes).

Quoted source text, attributed separately from HOL analysis.