Cmake/MSVC: Enable Edit and Continue for debug builds.

This change switches the debug symbol format from /Zi to /ZI for
debug builds of blender, allowing Edit and Continue to work.

This allows limited [1] code changes in the debugger without
having to stop the process and recompile a new binary leading
to improved developer productivity.

All MSVC versions we support support this flag, Clang on
windows does not mind the /ZI flag, but doesn't currently
emit the required information to have this feature work.

[1] https://docs.microsoft.com/en-us/visualstudio/debugger/supported-code-changes-cpp

Cleanup: Fix build error with MSVC

Previously eigens internal include order somehow implicitly provided
M_PI and friends. The recent eigen version bump broke this implicit
behaviour, better to be explicit that we need the math defines for MSVC.

Windows/deps: Add/fix openxr_sdk dependency

There were a few typos here and there, and the openxr_sdk does not respect the cflags we give it hence a patch was added to work around this undesirable behaviour.

Fix T55054: possible use of unsupported instructions in Cycles texture code

Differential Revision: https://developer.blender.org/D5326

Windows/MSI: Rework MSI installer.

The installer always upgraded the last version installed and did not allow for two versions to be installed side by side.

The reworked installer will allow side by side installs

install order:
```
2.81 -> 2.81a -> 2.82 : Allowed , will result in both 2.82 and 2.81a being installed
2.82 -> 2.81 -> 2.81a : Allowed , will result in both 2.82 and 2.81a being installed
2.82 -> 2.81a : Allowed , will result in both 2.82 and 2.81a being installed
2.82 -> 2.81a -> 2.81 : Not Allowed, 2.81 will only install if you manually remove 2.81a first.
```

Do note though that this will not apply to any previously issued installers and even for 2.80a this is not something we can fix.

This patch is for landing in 2.81 *only* and should be excluded from any possible 2.80a release.

Second change is a change to the compression level, building the MSI takes 30 minutes, which is crazy, perhaps worth it if the compression actually pays of.

```
MSI - none 1:35 247.0 MB (260,025,634 bytes)
MSI - mszip 2:02 89.6 MB ( 94,022,946 bytes)
MSI - low 2:35 81.6 MB ( 85,646,626 bytes)
MSI - medium 4:11 77.3 MB ( 81,136,930 bytes)
MSI - high 28:01 74.7 MB ( 78,384,418 bytes)

zip 1:32 93.2 MB ( 97,732,293 bytes)
7Z 2:22 65.0 MB ( 68,171,614 bytes)
```

It didn't, so I lowered it to medium, seemed reasonable.

Differential Revision: https://developer.blender.org/D5494

Reviewers: brecht, jesterking

Fix T56843 : fix case sensitive filenames on win10

When building with case sensitive folders there were some linker errors.

Windows: add cycles debug logging to helper batch file.

Windows/MSI: Rework MSI installer.

The installer always upgraded the last version installed and did not allow for two versions to be installed side by side.

The reworked installer will allow side by side installs

install order:
```
2.81 -> 2.81a -> 2.82 : Allowed , will result in both 2.82 and 2.81a being installed
2.82 -> 2.81 -> 2.81a : Allowed , will result in both 2.82 and 2.81a being installed
2.82 -> 2.81a : Allowed , will result in both 2.82 and 2.81a being installed
2.82 -> 2.81a -> 2.81 : Not Allowed, 2.81 will only install if you manually remove 2.81a first.
```

Do note though that this will not apply to any previously issued installers and even for 2.80a this is not something we can fix.

This patch is for landing in 2.81 *only* and should be excluded from any possible 2.80a release.

Second change is a change to the compression level, building the MSI takes 30 minutes, which is crazy, perhaps worth it if the compression actually pays of.

```
MSI - none 1:35 247.0 MB (260,025,634 bytes)
MSI - mszip 2:02 89.6 MB ( 94,022,946 bytes)
MSI - low 2:35 81.6 MB ( 85,646,626 bytes)
MSI - medium 4:11 77.3 MB ( 81,136,930 bytes)
MSI - high 28:01 74.7 MB ( 78,384,418 bytes)

zip 1:32 93.2 MB ( 97,732,293 bytes)
7Z 2:22 65.0 MB ( 68,171,614 bytes)
```

It didn't, so I lowered it to medium, seemed reasonable.

Differential Revision: https://developer.blender.org/D5494

Reviewers: brecht, jesterking

Windows: add cycles debug logging to helper batch file.

Fix T56843 : fix case sensitive filenames on win10

When building with case sensitive folders there were some linker errors.