base: Provide a getter for Fiber::started boolean variable

This can be used to check if the fiber has started its execution.

Change-Id: Ie9222b8076756363c9f82c1333c76a352bcaf817
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/18648
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

base: Rename TestFiber into SwitchingFiber

This is done since TestFiber is too generic and it is not the only
Fiber's testing subclass in the unit test

Change-Id: Idc386f487091ae9bdadae865090a6719a25583da
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19153
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

base: Rename unit test cc files to be *.test.cc.

This makes the name easier to read, looks ok if the file is named with
underscores between words or not, is easy to grep for, and shouldn't
introduce any ambiguities in the file names.

Change-Id: I34b7bcccea2d87c10c0de417dd5e3ef27c4b5666
Reviewed-on: https://gem5-review.googlesource.com/c/14676
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabeblack@google.com>