bug#66325: `inherit-input-method`'s poor behavior

[Ali AlipourR]

When you open a minibuffer with a non-nil inherit-input-method argument, the minibuffer will inherit its -default- input method from the parent buffer. This much is fine and desirable behavior. 

However, with this option enabled, you can no longer change your input method while editing inside the minibuffer. (i.e. using C-\ or toggle-input-method)

This is poor behavior, since if you are someone who uses input methods (i.e. uses emacs to write in languages other than English) you often want to use multiple input methods while editing inside a minibuffer.
For example, to enter a mixed English-Chinese/Arabic/Persian/... text as a search term etc.

Acceptable behavior would be if even with inherit-input-method enabled, Emacs allowed changing the input method inside the minibuffer (And just default to the input-method that it inherited from the parent buffer).

Optimal behavior would be if change of input-method inside a minibuffer also changed the current input method of the parent buffer, so that when you close the minibuffer and return to parent buffer, you have your last selected input method that you used inside the minibuffer, selected and ready to use inside the parent buffer. 

Sorry if the technical terms used aren't 100% accurate, as I'm still an Emacs newbie ...

Thanks,
Ali