RFR: 8364128: Improve gathering of cpu feature names using stringStream [v5]

[Ashutosh Mehra]

> This PR implements the code for cpu features names string using ~FormatBuffer~ stringStream. ~It also improves and extends FormatBuffer with an additional method that appends comma separated strings to the buffer.~ It also adds a method to stringStream that that appends separated strings separated by a delimiter to the buffer.  This is useful in creating the cpu features names string.
> This code will also be useful in Leyden to implement cpu feature check for AOTCodeCache [0].
> Platforms affected: x86-64 and aarch64
> Other platforms can be done if and when Leyden changes are ported to them.
> 
> [0] https://github.com/openjdk/leyden/pull/84

Ashutosh Mehra has updated the pull request incrementally with one additional commit since the last revision:

  Address review comments
  
  Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26515/files
  - new: https://git.openjdk.org/jdk/pull/26515/files/21383a7d..cca14916

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26515&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26515&range=03-04

  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/26515.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26515/head:pull/26515

PR: https://git.openjdk.org/jdk/pull/26515