RFR: 8297539: Use PrimitiveConversions::cast for local uses of the int<->float union conversion trick [v2]

[Afshin Zafari]

> **Only** the instances of using `union` for converting `int` to `float` are replaced with call to `PrimitiveConversions::cast<To>(From)` method. Some few cases with conversion of `long` <->`double` are also replaced with `PrimitiveConversions::cast<To>(From)`. The other instances where the union contains other types of fields than `int` and `float` are left unchanged.
> 
> ### Test
> local hotspot:tier1
> mach5 tiers 1-5

Afshin Zafari has updated the pull request incrementally with two additional commits since the last revision:

 - order of headers in includes.
 - order of headers corrected

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13136/files
  - new: https://git.openjdk.org/jdk/pull/13136/files/88e9a239..675997a7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13136&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13136&range=00-01

  Stats: 4 lines in 2 files changed: 2 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13136.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13136/head:pull/13136

PR: https://git.openjdk.org/jdk/pull/13136