RFR: 8297967: Make frame::safe_for_sender safer [v6]

[Johannes Bechberger]

> Makes `frame::safe_for_sender` safer by checking that the location of the return address, sender stack pointer, and link address is accessible. This makes the method safer in the case of broken frames.

Johannes Bechberger has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Remove errorneously added check
 - Remove check for value that might be null
 - More SafeFetch
 - Make frame::safe_for_sender safer with SafeFetch

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

Changes: https://git.openjdk.org/jdk/pull/11461/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11461&range=05
  Stats: 31 lines in 4 files changed: 25 ins; 2 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/11461.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/11461/head:pull/11461

PR: https://git.openjdk.org/jdk/pull/11461