Asset processor: separate modtime scanning tests (#7217)

* Move modtime scanning tests out of APM tests file and into its own file.

Changes were kept to a minimum to get things compiling, this is just a move of code

Signed-off-by: amzn-mike <80125227+amzn-mike@users.noreply.github.com>

* Fix rebase compile errors

Signed-off-by: amzn-mike <80125227+amzn-mike@users.noreply.github.com>

Code/Tools/AssetProcessor/native/tests/PathDependencyManagerTests.cpp

@@ -49,7 +49,7 @@ namespace UnitTests
     }
 
     struct PathDependencyBase
-        : UnitTest::TraceBusRedirector
+        : ::UnitTest::TraceBusRedirector
     {
         void Init();
         void Destroy();
@@ -65,7 +65,7 @@ namespace UnitTests
     };
 
     struct PathDependencyDeletionTest
-        : UnitTest::ScopedAllocatorSetupFixture
+        : ::UnitTest::ScopedAllocatorSetupFixture
         , PathDependencyBase
     {
         void SetUp() override
@@ -357,7 +357,7 @@ namespace UnitTests
     }
 
     struct PathDependencyBenchmarks
-        : UnitTest::ScopedAllocatorFixture
+        : ::UnitTest::ScopedAllocatorFixture
           , PathDependencyBase
     {
         static inline constexpr int NumTestDependencies = 4; // Must be a multiple of 4
@@ -530,7 +530,7 @@ namespace UnitTests
 
     BENCHMARK_F(PathDependencyBenchmarksWrapperClass, BM_DeferredWildcardDependencyResolution)(benchmark::State& state)
     {
-        for (auto _ : state)
+        for ([[maybe_unused]] auto unused : state)
         {
             m_benchmarks->m_stateData->SetProductDependencies(m_benchmarks->m_dependencies);