RFR: 8358533: Improve performance of java.io.Reader.readAllLines

[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.

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

Commit messages:
 - 8358533: Improve performance of java.io.Reader.readAllLines

Changes: https://git.openjdk.org/jdk/pull/25863/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25863&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358533
  Stats: 142 lines in 2 files changed: 130 ins; 10 del; 2 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