Re-vendor MAPI headers from microsoft/MapiStubLibrary

[Avasam]

Re-vendors MAPI headers and library from https://github.com/microsoft/MAPIStubLibrary

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The entirety of com/win32comext/mapi/src/MAPIStubLibrary/ is a direct copy of the source. Except for this text:

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These MAPI headers were downloaded from microsoft/MAPIStubLibrary@5183a5f and enable us to build the MAPI extension.

in com/win32comext/mapi/src/MAPIStubLibrary/README.md

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com/win32comext/mapi/src/extraMAPIDefs.h and com/win32comext/mapi/src/extraMAPIGuids.h have been moved out since they're not vendored files.

[mhammond]

This is great, thanks! Maybe later we could script this (although I guess the new location remains fairly static so probably not worth it yet)

[Avasam]

This is great, thanks! Maybe later we could script this (although I guess the new location remains fairly static so probably not worth it yet)

Given #2368 , I'm not too concerned about trying to stay actively in sync. It's also easy to just copy/paste an entire folder. But yeah, that could be done either through a vendoring script or git submodules.