This patch is a continuation of D11695 but this patch is independent.

Problem
IME conversion candidate window is displayed where the mouse click.

Ideally, the window is displayed below the cursor or text selection,

Blender need to tell the input method program where the conversion candidate window is during Japanese and Chinese input.

In macOS, the firstRectforCharacterRange is called when input by the input method starts, and the position of the conversion candidate window is specified.
Therefore, it is necessary to set the position of the conversion candidate window before input starts.
This patch changes it so that the position of the conversion candidate window is always set when the cursor is drawn.

I have confirmed that this patch does not affect East Asian input in Windows.
However, since my native language is Japanese, I have not done a detailed study of the effect on Chinese and Korean.
I need feedback from Chinese and Korean users.