refactor: Move sdk.Dec to math package (#12634)

## Description





---

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- [ ] 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
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- [ ] updated the relevant documentation or specification
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- [ ] 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 
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types/math.go

@@ -35,3 +35,40 @@ const (
 func (ip IntProto) String() string {
 	return ip.Int.String()
 }
+
+type (
+	Dec = sdkmath.LegacyDec
+)
+
+const (
+	Precision            = sdkmath.LegacyPrecision
+	DecimalPrecisionBits = sdkmath.LegacyDecimalPrecisionBits
+)
+
+var (
+	ZeroDec                  = sdkmath.LegacyZeroDec
+	OneDec                   = sdkmath.LegacyOneDec
+	SmallestDec              = sdkmath.LegacySmallestDec
+	NewDec                   = sdkmath.LegacyNewDec
+	NewDecWithPrec           = sdkmath.LegacyNewDecWithPrec
+	NewDecFromBigInt         = sdkmath.LegacyNewDecFromBigInt
+	NewDecFromBigIntWithPrec = sdkmath.LegacyNewDecFromBigIntWithPrec
+	NewDecFromInt            = sdkmath.LegacyNewDecFromInt
+	NewDecFromIntWithPrec    = sdkmath.LegacyNewDecFromIntWithPrec
+	NewDecFromStr            = sdkmath.LegacyNewDecFromStr
+	MustNewDecFromStr        = sdkmath.LegacyMustNewDecFromStr
+	MaxSortableDec           = sdkmath.LegacyMaxSortableDec
+	ValidSortableDec         = sdkmath.LegacyValidSortableDec
+	SortableDecBytes         = sdkmath.LegacySortableDecBytes
+	DecsEqual                = sdkmath.LegacyDecsEqual
+	MinDec                   = sdkmath.LegacyMinDec
+	MaxDec                   = sdkmath.LegacyMaxDec
+	DecEq                    = sdkmath.LegacyDecEq
+	DecApproxEq              = sdkmath.LegacyDecApproxEq
+)
+
+var _ CustomProtobufType = (*Dec)(nil)
+
+func (dp DecProto) String() string {
+	return dp.Dec.String()
+}