rpcclient: add getnewaddresstype and revert breaking change

[chappjc]

Since the address type was added to the btcjson and rpcclient packages, but the corresponding btcwallet PR is not yet merged, it made it clear that the rpcclient would ideally be able to work with older btcwallet versions. That is not straightforward with the recently modified rpcclient.Client methods. See #1843. This change seeks to make the rpcclient's GetNewAddress method compatible with both old and new btcwallet apps.

This reverts the previous breaking change to the GetNewAddress and GetRawChangeAddress rpcclient.Client methods, and adds the methods GetNewAddressType and GetRawChangeAddressType for requesting an address of a certain type. This change allows the rpcclient package to continue to work with versions of the btcwallet app that do not recognize the address type parameter.

An alternate change that does not add new methods but lets the type param be omitted is here: #1843 (comment) That keeps the current API with the breaking change however.

[coveralls]

Pull Request Test Coverage Report for Build 2168427285

• 0 of 30 (0.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 54.247%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
rpcclient/wallet.go	0	30	0.0%

Files with Coverage Reduction	New Missed Lines	%
rpcclient/wallet.go	2	0%

Totals
Change from base Build 2162753669:	-0.02%
Covered Lines:	25184
Relevant Lines:	46425

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💛 - Coveralls

[chappjc]

To summarize, this is primarily to allow latest rpcclient package to work with older btcwallet apps.

Could also achieve that with

// ... an empty addrType string will omit the type from the marshalled request.
func (c *Client) GetNewAddressAsync(account, addrType string) FutureGetNewAddressResult {
	aType := &addrType
	if addrType == "" {
		aType = nil
	}
	cmd := btcjson.NewGetNewAddressCmd(&account, aType)

Entirely depends on design goals for the btcwallet packages.

The change of the signature of GetNewAddress and GetNewAddressAsync introduced in 061aef9 is a smaller consideration IMO.

[Roasbeef]

LGTM 🦴

[chappjc]

Swinging back to btcsuite/btcwallet#783 now