RFR: 8297539: Consolidate the uses of the int<->float union conversion trick

[Afshin Zafari]

### Discussion

There are different ways of casting/converting integral types to floating point types and vice versa in the code. 
These conversions are changed to invocation of a centralised `cast<To>(From)` method in `primitiveConversions.hpp`. To make this changes build and run, some new `cast` methods are introduced and header dependencies changed. 

### Patch

- All instances of using `union` technique that are used for int<->float and long<->double type conversions are replaced by `PrimitiveConversions::cast<To>(From)` method.
  - Instances of, for example, converting `int`<->`intptr_t` are not changed.
- After this change, `JavaValue` also uses the `PrimitiveConversions::cast<To>(From)` templates. Therefore, all the `union` conversions for `int`<-> `float` and `long` <-> `double` in hotspot are now centralised in one location.
- Templates in `PrimitiveConversions` class are numbered from 1-9 and all lines of code that use `PrimitivEConversions::cast<To>(From)` have comments saying which templated `cast<To>(From)` matches. Issue number 8297539 is also in the comments to make the search/reviews more easier.
- The new 'cast<To>(From)' templates are numbered 6-9 for some instances where existing templates (1-5) did not match.
- `globalDefinitions.hpp` now includes `primitiveConversions.hpp`.
- `primitiveConversions.hpp` does NOT include `globalDefinitions.hpp` any more. Some typedef's are added to it to compensate the missing types.
- The followings are not changed:
  - `jni.hpp`
  - `ciConstant.hpp` is not changed, since uinon is not used for converting `int` <->`float` or `long` <-> `double`. There are some asserts that allow setter/getter used only for the same types.
  - `bytecodeInterpreter_zero.hpp` is not changed. Writing to and reading from the `VMJavaVal64` are always with the same type and no conversion is made.
  - union with bit fields are not changed.
  - `json.hpp` and `json.cpp` in src/hotspot/share/utilities.

### Test
mach5 tiers 1-5 passed, tiers 6-8 in progress

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Commit messages:
 - 8297539: Consolidate the uses of the int<->float union conversion trick

Changes: https://git.openjdk.org/jdk/pull/12384/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12384&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297539
  Stats: 404 lines in 12 files changed: 149 ins; 114 del; 141 mod
  Patch: https://git.openjdk.org/jdk/pull/12384.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12384/head:pull/12384

PR: https://git.openjdk.org/jdk/pull/12384