Add Android Runtime APEX bin directory to Bionic default shell search path.

Insert `/apex/com.android.runtime/bin` before `/system/bin` in the
default shell search path (`_PATH_DEFPATH`).

Test: Device boot test with Android Runtime APEX.
Test: Device boot test without Android Runtime APEX.
Test: cts-tradefed run cts --m vm-tests-tf
Test: cts-tradefed run cts --m CtsSimpleperfTestCases
Test: adb root && cts-tradefed run cts --m CtsBionicTestCases
Bug: 113373927
Bug: 119949783
Change-Id: I45fd6ccb939c7e99eb6bda740a7187774c1e930d