RFR: 8325340: Add ASCII fast-path to Data-/ObjectInputStream.readUTF [v6]

[Claes Redestad]

> Adding a fast-path for ASCII-only modified UTF-8 strings deserialied via Data- and ObjectInputStream
> 
> Testing: tier1-3

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

  Update src/java.base/share/classes/java/io/DataInputStream.java
  
  Co-authored-by: Raffaello Giulietti <raffaello.giulietti at oracle.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17734/files
  - new: https://git.openjdk.org/jdk/pull/17734/files/ca2b09c6..48902ad2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17734&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17734&range=04-05

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17734.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17734/head:pull/17734

PR: https://git.openjdk.org/jdk/pull/17734