Update typed arrays documentation

[dalexeev]

1. Extend the typed array constructor documentation.
2. Correct documentation of get_typed_*() methods.

The constructor is verbose and a bit confusing, I've seen questions about it on Discord several times.

• Closes Typed Array constructor has no clear documentation about how it should be used #79066.

[dalexeev]

Actually it returns Object#null, but I think it's a bug.

print(null) # <null>
print([].get_typed_script()) # <Object#null>

[dalexeev]

Now I'm not sure if this is a bug, this is the behavior of all Ref<T> properties and method return values. Should we draw the reader's attention to this difference?

var sprite := Sprite2D.new()
print(sprite.texture) # <Object#null>
print(sprite.texture == null) # true
print(is_same(sprite.texture, null)) # false
print(typeof(sprite.texture)) # 24
print(typeof(null)) # 0

Suggested change

	Returns the script associated with the typed array. This method returns a [Script] instance or [code]null[/code].
	Returns the script associated with the typed array. This method returns a [Script] instance (can be invalid).

[Mickeon]

Also see #69451 in the eventuality that it will be taken a look at.

[akien-mga]

Thanks!

[akien-mga]

Cherry-picked for 4.2.2.