RFR: 8276173: Clean up and remove unneeded casts in HeapDumper [v2]

[Leo Korinth]

> HeapDumper does a lot of unneeded casts. Some arguments should be const. Headers are not correctly sorted. Comment about identifier size on Windows and Solaris is not true.
> 
> First I cleaned up casting in the "union casting", but then I decided it was better to create a temporary bit_cast that we can use until we get the proper one in c++20.

Leo Korinth has updated the pull request incrementally with one additional commit since the last revision:

  restart failed github tests

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/6211/files
  - new: https://git.openjdk.java.net/jdk/pull/6211/files/9d963ef4..b8c97500

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=6211&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=6211&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6211.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6211/head:pull/6211

PR: https://git.openjdk.java.net/jdk/pull/6211