audio: WASAPI Force Shared Mode option (#745)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
This new option, `-wasapishared`, detects when the game opens WASAPI
Exclusive stream and forcibly opens a shared mode stream instead on the
real device.

#### Benefits of this:

1. No need for `force wasapi shared` patches
2. No need to change sample rate of audio devices before starting up
games
3. Adds ability to boot in shared mode even for games that do not have
shared wasapi changes (old GITADORA, popn HC)

As a result, this option is strictly better than `shared wasapi` patches
available for many games.

#### Downsides:
1. OS resampling will add a small latency, but not big enough to be
noticeable.
2. Using shared mode instead of exclusive mode adds latency, of course.

(If you cared about latency, you would use the low latency option, or
use exclusive or asio)

Basically it's the "make things work" button for audio that should work
for almost all games that we support.

The option has no effect if the game opens in shared mode.

## Testing
SDVX7 - ok
GITADORA GW - ok
popn HC - ok
IIDX - ok

src/spice2x/hooks/audio/audio.h

@@ -37,6 +37,12 @@ namespace hooks::audio {
     // minimum WASAPI exclusive buffer duration (milliseconds), if set. enlarges the device buffer
     // to avoid underrun crackle on endpoints that cannot service a tiny buffer in time.
     extern std::optional<uint32_t> EXCLUSIVE_BUFFER_MS;
+
+    // when true, WASAPI compatibility mode is active: exclusive-mode streams are redirected to
+    // shared mode. the Windows audio engine performs any required sample-rate / channel / bit-depth
+    // conversion, so the game's format is passed through unchanged and other applications can play
+    // audio simultaneously.
+    extern bool WASAPI_COMPATIBILITY_MODE;
     extern bool USE_DUMMY;
     extern WAVEFORMATEXTENSIBLE FORMAT;
     extern std::optional<Backend> BACKEND;