Refactor Instance management within the CallStack (take 2)

[Robbepop]

This refactor the CallStack so that Instance is no longer part of each CallFrame.

Instead the CallStack now has a dedicated stack for Instances and only pushes to this stack in case a function call changes the currently used Instance thus significantly reducing memory consumption for large call stacks.

Furthermore this optimizes returning from functions since now the cached linear memory and global only need to be re-loaded in case the returned call actually changed the currently used Instance which is an uncommon case and thus re-loading happens less frequently in the common case, speeding up call-intense workloads.

[codecov]

Codecov Report

Attention: Patch coverage is 77.92208% with 17 lines in your changes missing coverage. Please review.

Project coverage is 80.50%. Comparing base (f11e850) to head (ceade4e).

Files	Patch %	Lines
crates/collections/src/head_vec.rs	63.63%	8 Missing ⚠️
crates/wasmi/src/engine/executor/stack/calls.rs	85.18%	4 Missing ⚠️
crates/wasmi/src/engine/executor/instrs/call.rs	80.00%	3 Missing ⚠️
crates/wasmi/src/engine/executor/mod.rs	83.33%	1 Missing ⚠️
crates/wasmi/src/engine/executor/stack/mod.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1065      +/-   ##
==========================================
- Coverage   80.51%   80.50%   -0.02%     
==========================================
  Files         268      269       +1     
  Lines       24927    24970      +43     
==========================================
+ Hits        20070    20101      +31     
- Misses       4857     4869      +12     

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