RFR: 8264731: Introduce InstanceKlass::method_at_itable_or_null() [v2]

[Vladimir Ivanov]

> Introduce `InstanceKlass::method_at_itable_or_null()` - a non-throwing variant of `InstanceKlass::method_at_itable()` that implements interface method selection. 
> 
> As a cleanup, rewrite `InstanceKlass::method_at_itable()` on top of `InstanceKlass::method_at_itable_or_null()`.
> 
> Testing: 
> * [x] hs-tier1 - hs-tier6

Vladimir Ivanov has updated the pull request incrementally with one additional commit since the last revision:

  Cleanups

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3344/files
  - new: https://git.openjdk.java.net/jdk/pull/3344/files/2755b483..91b977c0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3344&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3344&range=00-01

  Stats: 6 lines in 1 file changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3344.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3344/head:pull/3344

PR: https://git.openjdk.java.net/jdk/pull/3344