RFR: 8266822: Rename MetaspaceShared::is_old_class to has_old_class_version [v6]

[Calvin Cheung]

> Please review this simple patch for renaming the function from `MetaspaceShared::is_old_class` to `MetaspaceShared::has_old_class_version`. Also added some comment to the function.
> 
> Tests:
> - [x] tier1, 2

Calvin Cheung has updated the pull request incrementally with one additional commit since the last revision:

  declare has_old_class_version as a const method

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3983/files
  - new: https://git.openjdk.java.net/jdk/pull/3983/files/ce372118..974e6c58

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3983&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3983&range=04-05

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3983.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3983/head:pull/3983

PR: https://git.openjdk.java.net/jdk/pull/3983