Allow more cross-referencing between run-test sources.

Allow all primary sources (src/, src-multidex/, src-aotex/,
src-bcpex/, src-ex/) to reference each other and jasmin*/
classes. Allow all replacement sources (src-art/, src2/,
src-ex2/) to reference the above classes.

The src/ folder needs to exist for this to take place, so
we moved src-art/ files to src/ in some tests.

As we're now compiling more files together into the `-cp`
folder "classes-tmp-all", classes defined in both src/
and src-ex/ would clash, so we moved the src-ex/ version
into src-ex2/.

Test: testrunner.py --host --optimizing --jvm
Test: testrunner.py --target --optimizing
Bug: 203171409
Change-Id: Ic890038b273f9ed7a99313f8d94323a2b612af43