Remove slice() length documentation caveats

[ghost]

What I did

Removed the caveats on not being allowed to use variables/immutables as length arguments for slice()

I think these applied in a previous version of Vyper, but as of at least v0.3.7 the restriction doesn't seem to apply anymore

How to verify it

Tests with variables for length arguments exist already in tests/parser/functions/test_slice.py, such as test_basic_slice()

A test_slice_immutable_length_arg() was also added to demonstrate that the functionality is available

Commit message

Remove slice() length documentation caveats

Description for the changelog

Remove slice() length documentation caveats

Cute Animal Picture

[codecov-commenter]

Codecov Report

Merging #3152 (96b588f) into master (fb50017) will decrease coverage by 37.36%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #3152       +/-   ##
===========================================
- Coverage   88.49%   51.13%   -37.37%     
===========================================
  Files          95       95               
  Lines       10778    10774        -4     
  Branches     2268     2202       -66     
===========================================
- Hits         9538     5509     -4029     
- Misses        797     4734     +3937     
- Partials      443      531       +88     

Impacted Files	Coverage Δ
vyper/builtin_functions/utils.py	0.00% <0.00%> (-100.00%)	⬇️
vyper/builtin_interfaces/ERC165.py	0.00% <0.00%> (-100.00%)	⬇️
vyper/builtin_interfaces/ERC4626.py	0.00% <0.00%> (-100.00%)	⬇️
vyper/builtin_interfaces/ERC20Detailed.py	0.00% <0.00%> (-100.00%)	⬇️
vyper/ir/s_expressions.py	5.88% <0.00%> (-88.24%)	⬇️
vyper/ast/natspec.py	12.34% <0.00%> (-86.42%)	⬇️
vyper/codegen/self_call.py	17.39% <0.00%> (-78.27%)	⬇️
vyper/codegen/external_call.py	19.29% <0.00%> (-78.08%)	⬇️
vyper/semantics/validation/levenshtein_utils.py	16.00% <0.00%> (-76.00%)	⬇️
vyper/ast/expansion.py	20.00% <0.00%> (-75.00%)	⬇️
... and 62 more

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[ghost]

Merging #3152 (96b588f) into master (fb50017) will decrease coverage by 37.36%.

Uhhh not sure about that 👀 issue with the bot maybe?

[fubuloubu]

Merging #3152 (96b588f) into master (fb50017) will decrease coverage by 37.36%.

Uhhh not sure about that 👀 issue with the bot maybe?

Some of the test suite is split up across multiple CI, it updates whenever the first one passes, and then keeps updating as other passes report status