feat: add DecApproxEq to decimal (#10592)

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## Description

Closes: #10500

Modified `decimal.go` to add a `DecApproxEq` function that checks to see if |d1 - d2| < tol for some `Dec` d1, d2, tol.  

---

### Author Checklist

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please add links to any relevant follow up issues.*

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

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your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

CHANGELOG.md

@@ -39,6 +39,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 
 ### Features
 
+* [\#10592](https://github.com/cosmos/cosmos-sdk/pull/10592) Add a `DecApproxEq` function that checks to see if `|d1 - d2| < tol` for some Dec `d1, d2, tol`.
 * [\#10393](https://github.com/cosmos/cosmos-sdk/pull/10393) Add `HasSupply` method to bank keeper to ensure that input denom actually exists on chain.
 * [\#9933](https://github.com/cosmos/cosmos-sdk/pull/9933) Introduces the notion of a Cosmos "Scalar" type, which would just be simple aliases that give human-understandable meaning to the underlying type, both in Go code and in Proto definitions.
 * [\#9884](https://github.com/cosmos/cosmos-sdk/pull/9884) Provide a new gRPC query handler, `/cosmos/params/v1beta1/subspaces`, that allows the ability to query for all registered subspaces and their respective keys.

types/decimal.go

@@ -801,3 +801,8 @@ func MaxDec(d1, d2 Dec) Dec {
 func DecEq(t *testing.T, exp, got Dec) (*testing.T, bool, string, string, string) {
 	return t, exp.Equal(got), "expected:\t%v\ngot:\t\t%v", exp.String(), got.String()
 }
+
+func DecApproxEq(t *testing.T, d1 Dec, d2 Dec, tol Dec) (*testing.T, bool, string, string, string) {
+	diff := d1.Sub(d2).Abs()
+	return t, diff.LTE(tol), "expected |d1 - d2| <:\t%v\ngot |d1 - d2| = \t\t%v", tol.String(), diff.String()
+}

types/decimal_test.go

@@ -7,6 +7,7 @@ import (
 	"math/big"
 	"testing"
 
+	"github.com/stretchr/testify/require"
 	"github.com/stretchr/testify/suite"
 	"sigs.k8s.io/yaml"
 
@@ -21,6 +22,29 @@ func TestDecimalTestSuite(t *testing.T) {
 	suite.Run(t, new(decimalTestSuite))
 }
 
+func TestDecApproxEq(t *testing.T) {
+	// d1 = 0.55, d2 = 0.6, tol = 0.1
+	d1 := sdk.NewDecWithPrec(55, 2)
+	d2 := sdk.NewDecWithPrec(6, 1)
+	tol := sdk.NewDecWithPrec(1, 1)
+
+	require.True(sdk.DecApproxEq(t, d1, d2, tol))
+
+	// d1 = 0.55, d2 = 0.6, tol = 1E-5
+	d1 = sdk.NewDecWithPrec(55, 2)
+	d2 = sdk.NewDecWithPrec(6, 1)
+	tol = sdk.NewDecWithPrec(1, 5)
+
+	require.False(sdk.DecApproxEq(t, d1, d2, tol))
+
+	// d1 = 0.6, d2 = 0.61, tol = 0.01
+	d1 = sdk.NewDecWithPrec(6, 1)
+	d2 = sdk.NewDecWithPrec(61, 2)
+	tol = sdk.NewDecWithPrec(1, 2)
+
+	require.True(sdk.DecApproxEq(t, d1, d2, tol))
+}
+
 // create a decimal from a decimal string (ex. "1234.5678")
 func (s *decimalTestSuite) mustNewDecFromStr(str string) (d sdk.Dec) {
 	d, err := sdk.NewDecFromStr(str)