[lworld] RFR: JDK-8234364: [lworld] ValueBootstrapMethods::isSubstitutable0 should do null check and type check

[Mandy Chung]

NPE was only reproducible with LW2 but not in LW3.   This patch adds null check and type check in
`ValueBootstrapMethods::isSubstitutable0` to ensure the invoker is called only when the parameters are non-null and of
the same type.

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Commit messages:
 - check if both arguments are null
 - Merge
 - [lworld] ValueBootstrapMethods::isSubstitutable0 should do null check and type check
 - Merge
 - Merge
 - revision per Roger's feedback
 - lambda metafactory supports inline widening/narrowing

Changes: https://git.openjdk.java.net/valhalla/pull/114/files
 Webrev: https://webrevs.openjdk.java.net/valhalla/114/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8234364
  Stats: 118 lines in 2 files changed: 111 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/114.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/114/head:pull/114

PR: https://git.openjdk.java.net/valhalla/pull/114