[idea] Extend prefix-mode ASCII input source switching to Windows (Korean IME)

[joonhwan]

Related: #380 (same idea for macOS)

idea / problem

On Windows with a Korean IME active, the same problem #380 describes for macOS
happens: after pressing the prefix key (Ctrl+B), the following keys (c, v,
h/j/k/l, ...) get composed into Hangul by the IME instead of being read as
prefix commands. switch_ascii_input_source_in_prefix currently only works on
macOS; on Windows it is a no-op.

requested change

Support switch_ascii_input_source_in_prefix on Windows too: while prefix mode
(and prefix-launched modes) is active, temporarily put the IME into ASCII input,
and restore it when returning to terminal input. At least for the Korean IME to
start with.

why you want this

Same UX gap as #380, just on Windows. Korean/CJK users on Windows hit the exact
same "prefix command gets eaten by the IME" problem, so the feature is
incomplete without the Windows side.

[joonhwan]

Though working in Windows Korean IME,now I am ready to PR. Could I get issue for this PR?

@ogulcancelik

[ogulcancelik]

approved, send pr please, ty!