Implement the Wasm custom-page-sizes proposal

[Robbepop]

Closes #1197.

• Introduces a MemoryTypeBuilder
  • The builder allows to set the Memory's page size.
• Use u32 instead of Pages type for MemoryType::{initial_pages, maximum_pages} methods.
  • This aligns the API better with Wasmtime's API.
• Now returns a proper error when the operating system ran out of heap memory to allocate in Memory::new and Memory::grow instead of panicking.
• Add MemoryType::{page_size, page_size_log2} methods.

ToDo

• Add Wasm spec tests for the Wasm custom-page-sizes proposal.
• Rename MemoryType::initial_pages to minimum.
• Rename MemoryType::maximum_pages to maximum.

Follow-Up Work

• Add Memory page count check to instantiation.
• Adjust Wasmi fuzzers to make use of custom-page-sizes.
• Use u64 instead of u32 in ...
  • Memory::new for minimum and maximum parameters.
  • MemoryType::new for minimum and maximum parameters.
  • MemoryTypeBuilder::min parameter
  • MemoryTypeBuilder::max parameter
  • MemoryType::minimum return type
  • MemoryType::maximum return type
  • MemoryType::page_size return type
  • Note: This allows the host to specify host-based linear memory with u32::MAX+1 pages which is valid for a page size of 1 byte.

The u64 parameters are important to align Wasmi with Wasmtime so that it also works here:

#[test]
fn it_works() {
    let mut b = wasmtime::MemoryType::builder();
    b.min(u64::from(u32::MAX) + 1);
    b.page_size_log2(0);
    b.build().unwrap(); // works!
}