refactor: Replace _.flatMap with Array.prototype.flatMap

[pjmattingly]

Addresses: #7747

[pjmattingly]

When addressing #7747 for _.flatmap, I noted that there were additional lodash calls that seemed similar. Both _.flattenDeep() and _.flattenDepth() can be replaced with Array.prototype.flat(); And so I took the liberty of making those small changes as well.

[codecov]

Codecov Report

Merging #11272 (d29f3d5) into main (2ac55b0) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main   #11272      +/-   ##
==========================================
- Coverage   85.89%   85.87%   -0.02%     
==========================================
  Files         315      315              
  Lines       13247    13273      +26     
==========================================
+ Hits        11378    11398      +20     
- Misses       1869     1875       +6     

Impacted Files	Coverage Δ
...ts/api-gateway/lib/hack/disassociate-usage-plan.js	100.00% <ø> (ø)
lib/cli/commands-schema/resolve-final.js	90.74% <100.00%> (ø)
lib/plugins/aws/invoke-local/index.js	69.87% <100.00%> (ø)
lib/plugins/aws/package/compile/events/http-api.js	96.65% <0.00%> (-0.05%)	⬇️
lib/cli/triage.js	91.34% <0.00%> (ø)
...ns/aws/package/compile/events/cognito-user-pool.js	100.00% <0.00%> (ø)
...urces/resources/cognito-user-pool/lib/user-pool.js	0.00% <0.00%> (ø)
...ib/plugins/aws/custom-resources/resources/utils.js	25.45% <0.00%> (+1.38%)	⬆️

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[pgrzesik]

Thanks @pjmattingly 🙇 I have one comment, please let me know what do you think

[pgrzesik]

Well done @pjmattingly 👏 Thank you 🙇