RFR: JDK-8254189: Improve comments for StackOverFlow and fix in_xxx() functions

[Thomas Stuefe]

Hi,

may I please have reviews for this small cleanup / fix?

While reviewing JDK-8253717 it was found that comments would help with understanding the StackOverFlow class. Especially the fact that the various _base_ are actually pointing outside their respective zone, since the stack grows downward and a zone (and the stack itself) range is [end, base). If you don't look at this code daily it can be surprising.

This also fixes some small off-by-one errors in various "in_stack_xxx_zone()" methods which test whether a given address is inside a zone and gave wrong results for address=base since base points outside its zone. This had the effect that an address could be in multiple zones.

Finally it adds a small gtest which tests the StackOverFlow methods.

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Commit messages:
 - Remove accidental newline
 - Initial patch

Changes: https://git.openjdk.java.net/jdk/pull/795/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=795&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254189
  Stats: 106 lines in 3 files changed: 103 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/795.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/795/head:pull/795

PR: https://git.openjdk.java.net/jdk/pull/795