This is a clean revert (no manual changes) of #2654 and the following #3255 (in reverse order). #3255 was a targeted fix (partial revert) for an incredibly disruptive bincompat bug, but #2654 has caused even more trouble. This full revert:

• Fixes ppltasks.cpp: Breaking change - New OLE32.dll import prevents process mitigations #3257, where the newly added dependency on ole32.dll was disruptive to certain exotic scenarios, and
• Fixes a "sandboxed process" scenario for the XStore team (reported by @vaboca), also disrupted by ole32.dll.
  • Don't ask me to explain this in any more detail, I don't know what's going on here. 🤯 That's the whole problem with this change - nobody fully understood the implications - and that's why we need to fully revert it, not mess around with it more.

By performing a full revert, we no longer need the partial revert. This returns us to the state that we successfully lived with in VS 2015 through VS 2022 17.2 inclusive.

@Scottj1s, the original author of #2654, agrees with the full revert here, and has confirmed that the original affected customer who needed that change has the ability to use a workaround in perpetuity.

🪞 The mirror of this PR, MSVC-PR-462260, additionally reverts the non-GitHub change in MSVC-PR-339372 affecting <ppltasks.h>.

❕ By changing ppltasks.cpp again, this affects the VCRedist. For the bincompat scenario involving mixing VS 2015, this should be unquestionably safe (the partial revert and the full revert result in the same behavior for the function in question, that's why the partial revert worked). For the question of when we can ship this fix, because it is urgently needed by the XStore team, we are planning to port this fix to VS 2022 17.6 before it reaches General Availability, which will require unlocking its redist, and then that unlocked redist will flow into VS 2022 17.7, so there should be no remaining mix-and-match nightmares (I hope).

I am not performing any other changes or cleanups at this time (I may come back to ppltasks.cpp in the future to add some #endif comments, but no logic changes, I have had a lifetime of being burned here).

I've filed #3606 to capture the vNext comments that are being reverted here.

⚠️ Note to self: Remember to start the 17.6 backport process after merging this.