Close #19378: address flaws in the new dis module APIs

- confusing line_offset parameter -> first_line parameter
- systematically test and fix new file parameter
- remove redundant Bytecode.show_info() API
- rename Bytecode.display_code() to Bytecode.dis() and have it
  return the multi-line string rather than printing it directly
- eliminated some not-so-helpful helpers from the bytecode_helper
  test support module

Also fixed a longstanding defect (worked around in the test suite)
where lines emitted by the dis module could include trailing white
space. That no longer happens, allowing the formatting tests to be
simplified to use plain string comparisons.

Lib/test/bytecode_helper.py

@@ -14,37 +14,6 @@ class BytecodeTestCase(unittest.TestCase):
         dis.dis(co, file=s)
         return s.getvalue()
 
-    def assertInstructionMatches(self, instr, expected, *, line_offset=0):
-        # Deliberately test opname first, since that gives a more
-        # meaningful error message than testing opcode
-        self.assertEqual(instr.opname, expected.opname)
-        self.assertEqual(instr.opcode, expected.opcode)
-        self.assertEqual(instr.arg, expected.arg)
-        self.assertEqual(instr.argval, expected.argval)
-        self.assertEqual(instr.argrepr, expected.argrepr)
-        self.assertEqual(instr.offset, expected.offset)
-        if expected.starts_line is None:
-            self.assertIsNone(instr.starts_line)
-        else:
-            self.assertEqual(instr.starts_line,
-                                expected.starts_line + line_offset)
-        self.assertEqual(instr.is_jump_target, expected.is_jump_target)
-
-
-    def assertBytecodeExactlyMatches(self, x, expected, *, line_offset=0):
-        """Throws AssertionError if any discrepancy is found in bytecode
-
-        *x* is the object to be introspected
-        *expected* is a list of dis.Instruction objects
-
-        Set *line_offset* as appropriate to adjust for the location of the
-        object to be disassembled within the test file. If the expected list
-        assumes the first line is line 1, then an appropriate offset would be
-        ``1 - f.__code__.co_firstlineno``.
-        """
-        actual = dis.get_instructions(x, line_offset=line_offset)
-        self.assertEqual(list(actual), expected)
-
     def assertInBytecode(self, x, opname, argval=_UNSPECIFIED):
         """Returns instr if op is found, otherwise throws AssertionError"""
         for instr in dis.get_instructions(x):