Add TEST_MAPPING file for FrameworkInputMethodSystemServerTests

To ensure FrameworkInputMethodSystemServerTests will be included in
presubmit tests and able to demote tests with FlakyTest/Ignore
annotation.

Also import this new TEST_MAPPING file path into IMF server
side's TEST_MAPPING file to ensure tests will be triggered when
modifying files in IMF server package.

Bug: 240359838
Test: atest FrameworkInputMethodSystemServerTests
Change-Id: Ia3594fddce01d822330b28571960e41f0de2d376