added letter_spacing attribute for TextStyle

[ariefendi992]

Example code

import flet
from flet import Page, Text, TextStyle


def main(page: Page):
    page.window_always_on_top = True
    page.add(
        Text(
            "Hello, world!\nHello, Flet",
            style=TextStyle(letter_spacing=6),
        )
    )
    page.update()


flet.app(target=main)

[CLAassistant]

All committers have signed the CLA.

[ndonkoHenri]

Thanks for your contribution!
The two properties you added are TextStyle properties - so I suggest we add them to the TextStyle dataclass instead.

[ndonkoHenri]

Thanks, @ariefendi992 ! I am merging...
Can you please make a PR here, adding this new property to the TextStyle docs?

[ariefendi992]

yes, i can.