RFR: 8358533: Improve performance of java.io.Reader.readAllLines [v6]

[Brian Burkhalter]

> Replaces the implementation `readAllCharsAsString().lines().toList()` with reading into a temporary `char` array which is then processed to detect line terminators and copy non-terminating characters into strings which are added to the list.

Brian Burkhalter has updated the pull request incrementally with one additional commit since the last revision:

  8358533: Test change accidentally omitted from previous commit

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25863/files
  - new: https://git.openjdk.org/jdk/pull/25863/files/0ee3f59c..ab959dfc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25863&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25863&range=04-05

  Stats: 19 lines in 1 file changed: 13 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/25863.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25863/head:pull/25863

PR: https://git.openjdk.org/jdk/pull/25863