Make "pending" block param act as "latest"

[lazartravica]

Fixes EVM-231.

Description

Changed the behaviour of functions that do:

• fetching blocks by Number/String/Hash
• decoding JSON-RPC requests
• fetching blocks by number

Changes include

• Bugfix (non-breaking change that solves an issue)
• Hotfix (change that solves an urgent issue, and requires immediate attention)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)

Checklist

• I have assigned this PR to myself
• I have added at least 1 reviewer
• I have added the relevant labels
• I have updated the official documentation
• I have added sufficient documentation in code

Testing

• I have tested this code with the official test suite
• I have tested this code manually

Manual tests

Ran various JSON-RPC queries with "pending" as the block parameter.

Documentation update

//TODO

[codecov]

Codecov Report

Merging #974 (31b7a27) into develop (461300f) will increase coverage by 1.03%.
The diff coverage is 86.74%.

❗ Current head 31b7a27 differs from pull request most recent head 8a49a83. Consider uploading reports for the commit 8a49a83 to get more accurate results

@@             Coverage Diff             @@
##           develop     #974      +/-   ##
===========================================
+ Coverage    52.91%   53.94%   +1.03%     
===========================================
  Files          129      132       +3     
  Lines        17113    17541     +428     
===========================================
+ Hits          9055     9463     +408     
- Misses        7411     7432      +21     
+ Partials       647      646       -1     

Impacted Files	Coverage Δ
jsonrpc/jsonrpc.go	25.53% <ø> (ø)
state/executor.go	3.63% <0.00%> (-0.34%)	⬇️
state/runtime/evm/instructions.go	15.80% <33.33%> (ø)
jsonrpc/debug_endpoint.go	78.35% <78.35%> (ø)
state/runtime/evm/state.go	73.60% <98.68%> (+8.78%)	⬆️
jsonrpc/codec.go	67.74% <100.00%> (-0.68%)	⬇️
jsonrpc/dispatcher.go	55.82% <100.00%> (+0.82%)	⬆️
jsonrpc/eth_endpoint.go	68.14% <100.00%> (-1.85%)	⬇️
jsonrpc/filter_manager.go	78.29% <100.00%> (+0.71%)	⬆️
jsonrpc/helper.go	100.00% <100.00%> (ø)
... and 5 more

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[vcastellm]

LGTM aside from @Stefan-Ethernal's comment