Fix: storage corruption from re-entrancy locks

[iamdefinitelyahuman]

What I did

Fix an issue allowing corruption of storage by re-entrancy locks.

In #2308, the location of re-entrancy locks was moved to the first unused storage slot. This worked fine as long as all multiple-slot types were stored using a sha3, but after #2361 this created a potential overlap between the lock slot and regular storage when the contract contains at least one storage value that occupies multiple slots.

How I did it

In vyper/parser/global_context.py, when calculating the offset for re-entrancy locks, correctly consider the size of each type.

How to verify it

Run the tests. I expanded a test that I'd added in #2361 that focuses on checking the layout of storage - it now also includes checks involving re-entrancy locks.

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[codecov-commenter]

Codecov Report

Merging #2379 (37d62d6) into master (d2f0a96) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2379      +/-   ##
==========================================
- Coverage   85.79%   85.74%   -0.06%     
==========================================
  Files          91       91              
  Lines        8992     8995       +3     
  Branches     2143     2145       +2     
==========================================
- Hits         7715     7713       -2     
- Misses        785      788       +3     
- Partials      492      494       +2     

Impacted Files	Coverage Δ
vyper/parser/global_context.py	68.65% <100.00%> (ø)
vyper/cli/vyper_compile.py	75.00% <0.00%> (-1.15%)	⬇️
vyper/functions/functions.py	88.36% <0.00%> (-0.39%)	⬇️

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[charles-cooper]

Based on offline conversation with @iamdefinitelyahuman it sounds like len(_globals) is not really used anymore for storage allocation; that's now handled here

vyper/vyper/context/validation/data_positions.py

Lines 20 to 28 in d2f0a96

	def set_storage_slots(vyper_module: vy_ast.Module) -> None:
	"""
	Parse module-level Vyper AST to calculate the layout of storage variables.
	"""
	available_slot = 0
	for node in vyper_module.get_children(vy_ast.AnnAssign):
	type_ = node.target._metadata["type"]
	type_.set_position(StorageSlot(available_slot))
	available_slot += math.ceil(type_.size_in_bytes / 32)

@iamdefinitelyahuman I think this change is fine so long as you comment that it's a kludge for not making the storage allocation info (from set_storage_slots) available to callers, AND add comments explaining that the other uses of len(_globals) are dead code. Thanks!