Added Debug trait for EmittedEvent

[abhi3700]

Issue raised in #1577.

Motivation:

Solution:
Added a Debug trait for EmittedEvent to view the details in unit tests

[codecov-commenter]

Codecov Report

Merging #1583 (97676ec) into master (8c5ee37) will decrease coverage by 6.23%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1583      +/-   ##
==========================================
- Coverage   71.61%   65.37%   -6.24%     
==========================================
  Files         205      205              
  Lines        6298     6293       -5     
==========================================
- Hits         4510     4114     -396     
- Misses       1788     2179     +391     

Impacted Files	Coverage Δ
crates/engine/src/test_api.rs	85.71% <ø> (ø)
crates/ink/ir/src/ir/contract.rs	0.00% <0.00%> (-100.00%)	⬇️
crates/ink/ir/src/ir/ink_test.rs	0.00% <0.00%> (-87.50%)	⬇️
crates/ink/ir/src/ir/trait_def/mod.rs	0.00% <0.00%> (-81.82%)	⬇️
crates/ink/ir/src/ir/storage_item/mod.rs	0.00% <0.00%> (-75.00%)	⬇️
crates/ink/ir/src/ir/storage_item/config.rs	0.00% <0.00%> (-68.75%)	⬇️
crates/ink/ir/src/ir/blake2.rs	20.83% <0.00%> (-58.34%)	⬇️
crates/ink/ir/src/ir/trait_def/config.rs	7.14% <0.00%> (-57.15%)	⬇️
crates/ink/ir/src/ir/trait_def/item/trait_item.rs	45.90% <0.00%> (-46.04%)	⬇️
crates/ink/ir/src/ir/config.rs	64.00% <0.00%> (-36.00%)	⬇️
... and 19 more

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[ascjones]

Thanks!