Move `ApplicationHome`, `ApplicationPid` and `ApplicationTemp` to the
`system` package. Since `system` package is now much lower level, the
existing `FileWriter` implementations also needed to move to prevent
package tangles.
Fixes gh-8614
Move projects to better reflect the way that Spring Boot is released.
The following projects are under `spring-boot-project`:
- `spring-boot`
- `spring-boot-autoconfigure`
- `spring-boot-tools`
- `spring-boot-starters`
- `spring-boot-actuator`
- `spring-boot-actuator-autoconfigure`
- `spring-boot-test`
- `spring-boot-test-autoconfigure`
- `spring-boot-devtools`
- `spring-boot-cli`
- `spring-boot-docs`
See gh-9316