Add README files for some subprojects and update various other docs (#8640)

Adds a section on design philosophy so we have something to point to
when people suggest features that aren't compatible with the way WPILib
is designed. Fixes some missed reorg changes (although the native-utils
link intentionally points to main as to be up-to-date in the future) and
generally cleans up any outdated information. Also includes wording
about supporting FTC. Per discussion in Slack, the LabVIEW wording has
been removed, and anything to do with LabVIEW is going to have to be
NI's job. And pursuant to #2757 and #5331, additional (light) developer
documentation has been added to some subprojects, mostly being a quick
summary of the what the project does and what it's for (or not for).

---------

Co-authored-by: sciencewhiz <sciencewhiz@users.noreply.github.com>
Co-authored-by: Joseph Eng <91924258+KangarooKoala@users.noreply.github.com>

wpigui/README.md

@@ -0,0 +1,9 @@
+# wpigui
+
+A [Dear Imgui](https://github.com/ocornut/imgui) wrapper that handles platform-specifics like the rendering API and adds some convenience functions. Bootstrap an app with three lines:
+
+```c++
+wpi::gui::CreateContext();
+wpi::gui::Initialize("Hello World", 1024, 768);
+wpi::gui::Main();
+```