Implement sticky section titles in tokens screens

[B3nz01d]

I've tested the accessibility context with this new implementation and in the Border token page, when browsing down the list, there is an issue when going back up.

https://github.com/user-attachments/assets/38ed5448-54f7-4cbf-b5cf-613d2ec46add

when on the last item before the title, it goes to the title, then one more up it goes to the theme selector and not the next item up. Is it possible to go up the page instead? what do you think @afrahB?

For accessibility, I also found:

• the text reading should read each list item token as one reading instead of reading each text separately
• the next item in the screen to read after the header is not the back, but the content within the page

[paulinea]

@B3nz01d Thank you for your tests. I will fix the first point in this PR. For the second one, this is the native behavior of sticky headers and Ludo told me it is the same behavior on iOS side. I suggest to create a specific issue for this point in order to avoid blocking this feature because it could be tricky to change. What do you think?