update:support declared function in classfile's overload decl

[luoliwoshang]

#1874
The overloaded function declaration in classfile will eventually become an overloaded method of type classfile

Rect.gox

func addString(a, b string) string {
	return a + b
}

func addInt(a, b int) int {
	return a + b
}

func add = (
	addInt
	addString
)

autogen.go

package main

const Gopo_Rect_add = ".addInt,.addString"

type Rect struct {
}

func (this *Rect) addString(a string, b string) string {
	return a + b
}
func (this *Rect) addInt(a int, b int) int {
	return a + b
}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.29%. Comparing base (01bb888) to head (d4c5639).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1875      +/-   ##
==========================================
+ Coverage   93.28%   93.29%   +0.01%     
==========================================
  Files          41       41              
  Lines       11612    11631      +19     
==========================================
+ Hits        10832    10851      +19     
  Misses        623      623              
  Partials      157      157              

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