RFR: 8287013: StringConcatFactory: remove short and byte mixers/prependers

[Claes Redestad]

The current short and byte mixers and prependers simply delegate to the int variants. At the LambdaForm level the values has already been implicitly cast to int, so removing this indirection and directly adapting to call the int-based variants is possible.

This is a cleanup with minimal effect on bootstrap overhead and peak performance, since all the LF logic only deals with basic types (where byte and short and other subword primitives has been widened to ints anyhow).

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Commit messages:
 - 8287013: StringConcatFactory: remove short and byte mixers/prependers

Changes: https://git.openjdk.java.net/jdk/pull/8786/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8786&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287013
  Stats: 87 lines in 2 files changed: 12 ins; 74 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8786.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8786/head:pull/8786

PR: https://git.openjdk.java.net/jdk/pull/8786