types: add Abs() method to sdk.Int

[hallazzang]

Fixes #8962

Description

Add Abs() method to sdk.Int.

closes: #8962

---

Before we can merge this PR, please make sure that all the following items have been
checked off. If any of the checklist items are not applicable, please leave them but
write a little note why.

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #8963 (bea1e9c) into master (56c312a) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head bea1e9c differs from pull request most recent head 9b32220. Consider uploading reports for the commit 9b32220 to get more accurate results

@@           Coverage Diff           @@
##           master    #8963   +/-   ##
=======================================
  Coverage   58.88%   58.88%           
=======================================
  Files         571      571           
  Lines       32118    32116    -2     
=======================================
- Hits        18912    18911    -1     
+ Misses      10984    10983    -1     
  Partials     2222     2222           

Impacted Files	Coverage Δ
types/int.go	72.91% <100.00%> (+0.38%)	⬆️
x/bank/keeper/send.go	83.62% <0.00%> (-0.87%)	⬇️
x/bank/keeper/keeper.go	72.91% <0.00%> (-0.28%)	⬇️
simapp/test_helpers.go	0.49% <0.00%> (+<0.01%)	⬆️

[alessio]

Ackd

[tac0turtle]

Thank you for the contribution!!

[orijbot]

Benchmark beginning. Status page: https://github.orijtech.com/benchmark/status?commit=8ee9da775ec6d66de0417a6a8a336c6eadc0bdef

[orijbot]

Benchmark finished. See the result: https://github.orijtech.com/benchmark/result?id=f79ac5bcdeae4f4bad3bfcd55d56c290