Ar/cor 2473 implement a default allocator for concordium std on wasm32

[allanbrondum]

Purpose

Set dlmalloc as the default allocator. It was default when compiling to https://doc.rust-lang.org/rustc/platform-support/wasm32-unknown-unknown.html with std library.

Changes

• dlmalloc is default
• bump_alloc feature enabled bump_alloc
• global_alloc is default and sets the global allocator
• updated concordium_std lib.rs docs for this change and the previous changes for wasm32v1 feature
• moved running internal wasm tests to concordium-std-internal-test, since it requires the cdylib crate type, which cannot be applied to concordium-std if it must be compilable without the global_alloc feature

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

[allanbrondum]

Moved to the end of the documentation

[limemloh]

Not sure when this feature is useful? Would the user ever want to disable default features and then enable just global_alloc alone? or any of the allocators without having global_alloc as well?
To me there seems to be 3 choices,

• none of the allocators enabled (disable default features)
• dlmalloc
• bump_alloc

[allanbrondum]

The combination I thought of was enabling bump_alloc but wanting to set it as global allocator yourself. The features dlmalloc and bump_alloc are truly additive, the global_alloc feature is not really additive (https://doc.rust-lang.org/cargo/reference/features.html#feature-unification). That can especially be relevant if you have several smart contracts in the same workspace. But it may be simpler not to have the feaute.

[allanbrondum]

Removed global_alloc feature, bump_alloc module is now compiled on WASM32 unconditionally