Build timings from auto-modularised VS solution with external and internal libs

To investigate how well modules work with MSVC without rewriting projects and putting up with malfunctioning intellisense, I made a little python script to modularise a whole VS solution (yes, *I* made it, using real bio-neurons).

The script lets me try out different modularisation strategies on a VS Solution on a per-project basis:

* Header-based, don't modularise. If dependencies are modules, they will be imported.
* PartitionsMI: Partition-per-header using standard module cpp units.
* PartitionsPI: Partition-per-header using MSVC partition cpp units.
* Submodules: Module-per-header
* SubmodulesII: Move implementation to interface (not always possible due to cyclic imports)

Modularised code is surrounded with `extern "C++" { export {`.

The code is a super secret incomplete game engine/game. But here's some info:

* External libs, including: Boost (unordered flat map), std, d3d, imgui, physx, spdlog, <windows>.
* Wrapper module for each.
* Solution projects: CommonStuff, Scripting, GameData, Graphics, Anim, SceneGraph, SceneManager, Entity, App
* Some projects don't have much code. Others have quite a bit. Enough to give the build system something to parallelise.

All projects built using debug config. Benchmarks average 3 or more timings, outliers ignored. CPU is 12600, 12 threads. Multipliers are speedup.

| |CommonStuff|Scripting|GameData|Graphics|Anim|SceneGraph|SceneManager|Entity|
|:-|:-|:-|:-|:-|:-|:-|:-|:-|
|Header-based, no pch|4.59s|5.68s|7.46s|2.92s|40.74s|24.94s|2.86s|3.19s|
|Header-based, pch|3.61s|5.30s|6.55s||19.38s|12.53s|||
|Extlib modules + CommonStuff submodules||3.60s|4.78s|1.62s|18.55s|9.41s|1.57s|2.09s|
|PartitionsMI|4.25s||8.09s|2.54s|||||
|PartitionsPI|4.02s|6.04s|7.09s|2.53s|33.83s|15.97s|2.66s|4.10s|
|Submodules|3.59s|4.75s|6.05s|2.26s|26.80s|14.31s|2.12s|3.15s|
|SubmodulesII|3.44s||7.93s||||||

| |CommonStuff|Scripting|GameData|Graphics|Anim|SceneGraph|SceneManager|Entity|
|:-|:-|:-|:-|:-|:-|:-|:-|:-|
|Header-based, no pch|1.00x|1.00x|1.00x|1.00x|1.00x|1.00x|1.00x|1.00x|
|Header-based, pch|1.27x|1.07x|1.14x||2.10x|1.99x|||
|Extlib modules + CommonStuff submodules||1.58x|1.56x|1.80x|2.20x|2.65x|1.82x|1.53x|
|PartitionsMI|1.08x||0.92x|1.15x|||||
|PartitionsPI|1.14x|0.94x|1.05x|1.15x|1.20x|1.56x|1.08x|0.78x|
|Submodules|1.28x|1.20x|1.23x|1.29x|1.52x|1.74x|1.35x|1.01x|
|SubmodulesII|1.33x||0.94x||||||

| |App|Single file|Full Rebuild| |App|Single file|Full Rebuild|
|:-|:-|:-|:-|:-|:-|:-|:-|
|Header-based, no pch|65.19s|3.97s|145.49s||1.00x|1.00x|1.00x|
|Header-based, app pch|24.74s|2.15s|108.92s||2.64x|1.85x|1.34x|
|Header-based, mostly pch|||78.87s||||1.84x|
|Extlib modules|26.82s|2.35s|58.89s||2.43x|1.69x|2.47x|
|Extlib modules + CommonStuff partitions|25.89s|2.47s|||2.52x|1.61x||
|Extlib modules + CommonStuff submodules|24.53s|2.23s|57.50s||2.66x|1.78x|2.53x|
|Extlib modules + most libs as submodules|31.14s|2.97s|||2.09x|1.34x||
|Full submodules, except app|34.61s|2.95s|88.90s||1.88x|1.35x|1.64x|
|Full submodules|64.02s|6.22s|142.98s||1.02x|0.64x|1.02x|

* "Most libs" = CommonStuff + Scripting + GameData + Graphics + Anim + SceneGraph.
* "Mostly pch" = PCH for CommonStuff, Scripting, GameData, Anim, SceneGraph, App.
* "Single file" is recompiling one moderately complex file in App. \~930 lines, lots of includes.
* "Full Rebuild" excludes extlib module wrappers.

Detailed timings of CommonStuff:

Header-based:

1> 210 ms LIB 1 calls
1> 4459 ms CL 2 calls
04.874 seconds

PartitionsMI:

1> 125 ms LIB 1 calls
1> 199 ms MSBuild 16 calls
1> 269 ms CppClean 1 calls
1> 798 ms SetModuleDependencies 10 calls
1> 1232 ms CL 2 calls
1> 1439 ms MultiToolTask