EDSC: move FileCheck tests into the source file

EDSC provide APIs for constructing and modifying the IR.  These APIs are
currently tested by a "test" module pass that reads the dummy IR (empty
functions), recognizes certain function names and injects the IR into those
functions based on their name.  This situation is unsatisfactory because the
expected outcome of the test lives in a different file than the input to the
test, i.e. the API calls.

Create a new binary for tests that constructs the IR from scratch using EDSC
APIs and prints it.  Put FileCheck comments next to the printing.  This removes
the need to have a file with dummy inputs and assert on its contents in the
test driver.  The test source includes a simplistic test harness that runs all
functions marked as TEST_FUNC but intentionally does not include any
value-testing functionality.

PiperOrigin-RevId: 235886629