Split pip tests in different modules to enable sharding and reduce runtime

Temporarily keep a `WMShellPipTests` module for compatibility with the presubmit configuration. This will be removed in a future CL after presubmit is updated to avoid causing instability

Bug: 301574363
Test: atest WMShellFlickerTestsPip
Change-Id: I3aa7de019ec1d2a0871206499bbc59fdf6677bf6