[core:encoding/json] When Unmarshalling, Only Match On Struct Tags If Present

[dozn]

Context

If a struct field contains a struct tag, we should only match on the tag.
https://godbolt.org/z/TcP3974vK

package main

import "core:encoding/json"
import "core:fmt"

main :: proc() {
    JSON := `{"same": 1}`
    s: struct {same: int `json:"different"`}
    json.unmarshal(transmute([]u8)JSON, &s)
    fmt.println(s)
}

Expected

S{same = 0}

Actual

S{same = 1}

What Else I've Done

• added a comment for json_name_from_tag_value, because I omitted it from a previous commit due to not understanding why it's useful (and fixed a small bug that caused, where struct tags which also contained an omitempty would not work correctly)
• moved the inline function field_test beside the only place it's used