Add ability to set values by path

[phplego]

This commit adds Value.SetP and Value.GetP methods.

Motivation

These methods provide a straightforward way to access and modify deeply nested JSON structures without the need for repetitive checks and object creations. They enhance the usability of the fastjson package by allowing developers to work with JSON paths directly.

Usage Intended:

• SetP(path Path, value *Value): Sets a value at the specified JSON path, creating any necessary intermediate objects or arrays along the way.

• GetP(path Path) *Value: Retrieves a value from the specified JSON path, returning nil if any part of the path does not exist.

Example

v := fastjson.MustParse(`{"a": {"b": 1}}`)

// Set a nested value
v.SetP([]any{"a", "b"}, fastjson.MustParse("2"))
// Now v is: {"a": {"b": 2}}

// Get a nested value
val := v.GetP([]any{"a", "b"}).GetInt()
// val == 2

// Set a new nested value, creating intermediate objects
v.SetP([]any{"a", "c", "d"}, fastjson.MustParse(`"hello"`))
// Now v is: {"a": {"b": 2, "c": {"d": "hello"}}}