Add tkinter Canvas methods rotate and rchars

[serhiy-storchaka]

Two Tk canvas widget commands have no tkinter wrapper and are currently reachable only through tk.call().

• rchars (since Tk 8.6) replaces the characters (for text items) or coordinates (for line and polygon items) in a given index range with a new value, complementing the already wrapped dchars and insert.
• rotate (new in Tk 9.0) rotates the coordinates of items about an origin by a given angle, complementing the already wrapped move and scale.

I propose to add the corresponding Canvas.rchars() and Canvas.rotate() methods.

Linked PRs

• gh-151876: Add tkinter Canvas methods rotate and rchars #151877