cmd/compile: support go local variables

[xiandaonancheng]

This Mr contains two ways to create go local variables that only have one instance for each goroutine:
1、export a function "runtime.NewGoLocal" to create go local variable by given key.
2、add a syntax token "go_local", just like "thread_local" in c++.

For 1, developers can create the same object in different scopes. example as below, a and b are the same object in one goroutine:
func goLocalA(){
a,_ := runtime.NewGoLocal[int]("go local", func() int {
return 10
})
a.Val++
fmt.Println(a.Val)
}

func goLocalB(){
    b,_ := runtime.NewGoLocal[int]("go local", func() int {
	    return 10
    })
    b.Val++
    fmt.Println(b.Val)
}

For 2, developers can define variables like "var", each variable is unique. These variables will be initialized only once in the same goroutine. example:
func goLocalVar() {
go_local a int = 100
a++
fmt.Println(a)
}

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[gopherbot]

Message from Keith Randall:

Patch Set 1: Hold+1

(1 comment)

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This PR is being closed because golang.org/cl/612716 has been abandoned.

This CL is against the 1.23 branch. Our approach is to only take CLs on the main branch.