RFR: 8253162: Make frame::oops_do const

[Stefan Karlsson]

Make frame::oops_do const, so that we can use a const frame& receiver when appropriate. With this, we can get rid of
the temporary copies made just to make the frame variable non-const. See for example:
https://github.com/openjdk/zgc/blob/c4765b5599d07124410f8a80b1acef9349a998e0/src/hotspot/share/gc/z/zStackWatermark.cpp#L96

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Commit messages:
 - Make frame::oops_do const

Changes: https://git.openjdk.java.net/jdk/pull/175/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=175&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253162
  Stats: 35 lines in 2 files changed: 0 ins; 1 del; 34 mod
  Patch: https://git.openjdk.java.net/jdk/pull/175.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/175/head:pull/175

PR: https://git.openjdk.java.net/jdk/pull/175