RFR: 8331724: Refactor j.l.constant implementation to internal package [v6]

[Claes Redestad]

> This PR suggests refactoring the implementation classes of java.lang.constant into a new package jdk.internal.constant to enable sharing some trusted static factory methods with users elsewhere in java.base, such as java.lang.invoke and java.lang.classfile. The refactoring also adds some "trusted" methods for use when input is pre-validated, and makes use of them where applicable in the current implementation. There are more changes in the pipeline which will be folded into #17108 or PR'ed once that is integrated. 
> 
> There are two optimizations mixed up here. One in `MethodTypeDesc.ofDescriptor`:
> 
> Name                                                             (descString) Cnt     Base     Error      Test   Error  Unit  Change
> MethodTypeDescFactories.ofDescriptor  (Ljava/lang/Object;Ljava/lang/String;)I   6  138,371 ±   0,767   136,939 ± 1,126 ns/op   1,01x (p = 0,000*)
> MethodTypeDescFactories.ofDescriptor                                      ()V   6   10,528 ±   2,495     4,110 ± 0,047 ns/op   2,56x (p = 0,000*)
> MethodTypeDescFactories.ofDescriptor ([IJLjava/lang/String;Z)Ljava/util/List;   6  209,390 ±   4,583   196,175 ± 3,211 ns/op   1,07x (p = 0,000*)
> MethodTypeDescFactories.ofDescriptor                    ()[Ljava/lang/String;   6   36,039 ±   8,684    20,794 ± 1,110 ns/op   1,73x (p = 0,000*)
> MethodTypeDescFactories.ofDescriptor                                 (..IIJ)V   6  279,139 ±   6,248   187,934 ± 0,857 ns/op   1,49x (p = 0,000*)
> MethodTypeDescFactories.ofDescriptor                 (.....................).   6 2174,387 ± 132,879  1150,652 ± 3,158 ns/op   1,89x (p = 0,000*)
>   * = significant
> 
> 
> The other in `ClassDesc::nested`, where to get rid of a simple static method in `ConstantUtils` I ended up speeding up and simplifying the public factory method:
> 
> Name                                      Cnt    Base     Error    Test   Error  Unit  Change
> ClassDescFactories.ReferenceOnly.ofNested   6 209,853 ± 132,525  22,017 ± 0,573 ns/op   9,53x (p = 0,000*)
>   * = significant
> 
> 
> The optimizations could be split out and PRd independently, but I think they are simple enough to include in this refactoring.

Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:

  Validate after copying to avoid TOCTOU

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/19105/files
  - new: https://git.openjdk.org/jdk/pull/19105/files/eb23cf51..b21d3e60

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=19105&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=19105&range=04-05

  Stats: 10 lines in 1 file changed: 6 ins; 3 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/19105.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19105/head:pull/19105

PR: https://git.openjdk.org/jdk/pull/19105