[bugfix] normalize paths to enable running external tests

[joeljeske]

Description

Normalize file paths before passing them to runfiles.rlocation() within the test runner.

Before this change, you could not execute a bazel test target that is not in the primary workspace, it would error with

For example running bazel run @my_external_repo//my/path/to:test

Exception in thread "main" java.lang.reflect.InvocationTargetException
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at com.google.testing.coverage.JacocoCoverageRunner.main(JacocoCoverageRunner.java:592)
Caused by: java.lang.IllegalArgumentException: path is not normalized: "my_workspace/../my_external_repo/my/path/to/test/test.args"
	at com.google.devtools.build.runfiles.Util.checkArgument(Util.java:45)
	at com.google.devtools.build.runfiles.Runfiles.rlocation(Runfiles.java:337)
	at io.bazel.rulesscala.scala_test.Runner.extendFromFileArgs(Runner.java:51)
	at io.bazel.rulesscala.scala_test.Runner.extendArgs(Runner.java:37)
	at io.bazel.rulesscala.scala_test.Runner.main(Runner.java:33)
	... 5 more

Motivation

We should be able to run tests from external repos

[liucijus]

Thanks, @joeljeske!