RFR: 8377388: Replacing "new StringReader(String)" by "Reader.of(CharSequence);" in Scanner

[Markus KARG]

This Pull Request provides an implementation for [JDK-8377388](https://bugs.openjdk.org/browse/JDK-8377388): 'Replacing "new StringReader(String)" by "Reader.of(CharSequence);" in Scanner'.

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Commit messages:
 - 8377388: Replacing "new StringReader(String)" by "Reader.of(CharSequence);" in Scanner

Changes: https://git.openjdk.org/jdk/pull/29627/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29627&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377388
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/29627.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29627/head:pull/29627

PR: https://git.openjdk.org/jdk/pull/29627