RFR: 8316514: Better diagnostic header for VtableStub

[Aleksey Shipilev]

Similar to [JDK-8316178](https://bugs.openjdk.org/browse/JDK-8316178), but for VtableStubs. JMH perfasm would like to know where the stub code ends.

Printout before this fix:


Decoding VtableStub vtbl[5]@281473683415027
--------------------------------------------------------------------------------
  0x0000ffff9bf22320:   ldr     w16, [x1, #8]
  0x0000ffff9bf22324:   movk    x16, #0x98, lsl #32
  0x0000ffff9bf22328:   ldr     x12, [x16, #496]
  0x0000ffff9bf2232c:   ldr     x8, [x12, #64]
  0x0000ffff9bf22330:   br      x8
  0x0000ffff9bf22334:   udf     #0


Printout after this fix:


--------------------------------------------------------------------------------
Decoding VtableStub vtbl[5]@281473592893427 [0x0000ffff97f22320, 0x0000ffff97f22338] (24 bytes)
--------------------------------------------------------------------------------
  0x0000ffff97f22320:   ldr     w16, [x1, #8]
  0x0000ffff97f22324:   eor     x16, x16, #0x3800000000
  0x0000ffff97f22328:   ldr     x12, [x16, #496]
  0x0000ffff97f2232c:   ldr     x8, [x12, #64]
  0x0000ffff97f22330:   br      x8
  0x0000ffff97f22334:   udf     #0

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

Commit messages:
 - Fix

Changes: https://git.openjdk.org/jdk/pull/15816/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15816&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316514
  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/15816.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15816/head:pull/15816

PR: https://git.openjdk.org/jdk/pull/15816