Omr: Properly anchor and validate rdbar nodes introduced late in compilation

[andrewcraik]

In some modes we introduce rdbar nodes late in the compile. These nodes need to properly anchored otherwise issues like that fixed in #3080 occur. This is to track adding a verification pass to ensure rdbar nodes are properly anchored and any additional changes to ensure late addition of rdbars are also anchored correctly. Once done #3080 may be reverted or left at the project's discretion. I believe @yanluo7 is taking a look at what is needed in this area.

[cathyzhyi]

https://github.com/eclipse/omr/pull/3438 inserts a pass in lowertree to fix unanchored rdbars.
furture work includes:

1. Add proper verification in ILValidator
2. fix rdbars introduced later in compilation (mostly optimizer)

[dchopra001]

I hit that assert introduced by #3438 inside a unit test. I'm attaching a trace log that details the failing compilation. Looks like one of the rdbar nodes generated Post Inlining is not anchored properly.
trace.log