[code-reflection] Integrated: Allow static access to layouts of iface mapped segments

[Gary Frost]

Previously we needed an instance of an iface mapped segment in order to access it's layout. 

Moving towards a pattern that allows us to access this information from the iface interface class.  

We will need this to allow us to capture offsets when lowereing to SSA form.

-------------

Commit messages:
 - Allow static access to layouts of iface mapped segments

Changes: https://git.openjdk.org/babylon/pull/137/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=137&range=00
  Stats: 273 lines in 32 files changed: 139 ins; 53 del; 81 mod
  Patch: https://git.openjdk.org/babylon/pull/137.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/137/head:pull/137

PR: https://git.openjdk.org/babylon/pull/137