Move various "examples" into snippets. Several examples that were less
than a full mechanism or robot were moved to snippets. `arcadedrive` and
`tankdrive` were removed in favor of their Gamepad variants. `hidrumble`
was removed due to being too simple. `potentiometerpid` was removed
because of low utility. `gyromecanum` replaced `mecanumdrive` for
deduplication and because very few teams run holonomic drivetrains
without gyros.
This enables frc-docs to use RLIs for things that are currently in-line
code blocks, and ensures they compile, which is important with the 2027
breaking changes coming. They are kept separate from the examples to
ensure they don't polute the VSCode examples finder.
Adds the Encoder snippets used in the frc-docs Encoder article as the
first instance of this.
This fixes the following compilation errors:
```
/home/tav/frc/wpilib/allwpilib/wpilibcExamples/src/main/cpp/examples/UnitTest/cpp/subsystems/Intake.cpp:5:10: fatal error: subsystems/Intake.h: No such file or directory
5 | #include "subsystems/Intake.h"
| ^~~~~~~~~~~~~~~~~~~~~
/home/tav/frc/wpilib/allwpilib/wpilibcExamples/src/test/cpp/examples/UnitTest/cpp/subsystems/IntakeTest.cpp:11:10: fatal error: Constants.h: No such file or directory
11 | #include "Constants.h"
| ^~~~~~~~~~~~~
```
