RFR: 8298241: Replace C-style casts with JavaThread::cast [v2]

[David Holmes]

> This is a simple cleanup RFE to get rid of old-style C casts in relation to JavaThread.
> 
> In many cases involving NULL/nullptr the cast could just be dropped. Sometimes a static cast is needed to disambiguate overloads.
> 
> A couple of reinterpret_cast are needed when doing int/ptr conversion.
> 
> static_cast is used for void* conversion.
> 
> The other changes should be self explanatory.
> 
> The changes in
> 
> src/hotspot/os_cpu/bsd_aarch64/javaThread_bsd_aarch64.cpp
> src/hotspot/os_cpu/windows_aarch64/javaThread_windows_aarch64.cpp
> 
> are a bit more extensive. That code was using an alias for `this` which is completely unnecessary (and the alias creation was using the cast). This could be factored out if thought necessary.
> 
> I grep'd as best I could for the old C-style casts but can't be certain I got them all.
> 
> Testing: 
>  - all builds in our tiers1-5
>  - local linux x64 product, slowdebug and fastdebug
>  - GHA
>  - Sanity testing tiers 1-3
> Thanks.

David Holmes has updated the pull request incrementally with one additional commit since the last revision:

  Fixed commented examle.

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/11682/files
  - new: https://git.openjdk.org/jdk/pull/11682/files/5641507a..34f2745d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11682&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11682&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11682.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11682/head:pull/11682

PR: https://git.openjdk.org/jdk/pull/11682