add sub context to support combining nested automap and rename

[goghcrow]

When I Combine automap and fieldmap, it doesn't work

// goverter:converter
type Converter interface {
	// goverter:map . Address
	// goverter:map Street Address.StreetName
	Convert(FlatPerson) Person
}

type FlatPerson struct {
	Name    string
	Age     int
	Street  string
	ZipCode string
}

type Person struct {
	Name string
	Age  int
	Address
}
type Address struct {
	StreetName string
	ZipCode    string
}

the error message was as follows

| github.com/jmattheis/goverter/example/nested.FlatPerson
|
|      | goverter:map . Address
|      |
|      |
|      |
source.       .???
target.Address.StreetName
|      |       |
|      |       | string
|      |
|      | github.com/jmattheis/goverter/example/nested.Address
|
| github.com/jmattheis/goverter/example/nested.Person

Cannot match the target field with the source entry: "StreetName" does not exist.

The solution might be to add the sub context when createing subMethod

It works fine.

package generated

import nested "github.com/jmattheis/goverter/example/nested"

type ConverterImpl struct{}

func (c *ConverterImpl) Convert(source nested.FlatPerson) nested.Person {
	var nestedPerson nested.Person
	nestedPerson.Name = source.Name
	nestedPerson.Age = source.Age
	nestedPerson.Address = c.nestedFlatPersonToNestedAddress(source)
	return nestedPerson
}
func (c *ConverterImpl) nestedFlatPersonToNestedAddress(source nested.FlatPerson) nested.Address {
	var nestedAddress nested.Address
	nestedAddress.StreetName = source.Street
	nestedAddress.ZipCode = source.ZipCode
	return nestedAddress
}

It works fine, too, and even handles nested cases. But I don't know if there are other problems

// goverter:converter
type Converter interface {
	// goverter:map . Address
	// goverter:map . Address.StreetInfo
	// goverter:map Street Address.StreetInfo.Name
	Convert(FlatPerson) Person
}

type FlatPerson struct {
	Name    string
	Age     int
	Street  string
	ZipCode string
}

type Person struct {
	Name string
	Age  int
	Address
}
type Address struct {
	StreetInfo
	ZipCode string
}
type StreetInfo struct {
	Name string
}

generated

package generated

import nested "github.com/jmattheis/goverter/example/nested"

type ConverterImpl struct{}

func (c *ConverterImpl) Convert(source nested.FlatPerson) nested.Person {
	var nestedPerson nested.Person
	nestedPerson.Name = source.Name
	nestedPerson.Age = source.Age
	nestedPerson.Address = c.nestedFlatPersonToNestedAddress(source)
	return nestedPerson
}
func (c *ConverterImpl) nestedFlatPersonToNestedAddress(source nested.FlatPerson) nested.Address {
	var nestedAddress nested.Address
	nestedAddress.StreetInfo = c.nestedFlatPersonToNestedStreetInfo(source)
	nestedAddress.ZipCode = source.ZipCode
	return nestedAddress
}
func (c *ConverterImpl) nestedFlatPersonToNestedStreetInfo(source nested.FlatPerson) nested.StreetInfo {
	var nestedStreetInfo nested.StreetInfo
	nestedStreetInfo.Name = source.Street
	return nestedStreetInfo
}

[jmattheis]

As described in #80 (comment). The changes have some edge-cases that aren't properly handled