docs(x/feegrant): use coins instead of tokens (#12444)

## Description

Closes: #12422 



---

### Author Checklist

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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
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/main/CONTRIBUTING.md#pr-targeting))
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- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/main/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/main/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)

api/cosmos/feegrant/v1beta1/feegrant.pulsar.go

@@ -2597,15 +2597,15 @@ const (
 	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
 )
 
-// BasicAllowance implements Allowance with a one-time grant of tokens
+// BasicAllowance implements Allowance with a one-time grant of coins
 // that optionally expires. The grantee can use up to SpendLimit to cover fees.
 type BasicAllowance struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
 	unknownFields protoimpl.UnknownFields
 
-	// spend_limit specifies the maximum amount of tokens that can be spent
-	// by this allowance and will be updated as tokens are spent. If it is
+	// spend_limit specifies the maximum amount of coins that can be spent
+	// by this allowance and will be updated as coins are spent. If it is
 	// empty, there is no spend limit and any amount of coins can be spent.
 	SpendLimit []*v1beta1.Coin `protobuf:"bytes,1,rep,name=spend_limit,json=spendLimit,proto3" json:"spend_limit,omitempty"`
 	// expiration specifies an optional time when this allowance expires