[jdk11u-dev] RFR: 8212597: Optimize String concatenation setup when using primitive operands

[Anton Bobrov]

This is a backport of b3b41df70fb5ec3187d165786b3c8ad2d4b4012b / [JDK-8212597](https://bugs.openjdk.org/browse/JDK-8212597)

This backport is needed to facilitate clean backports of various String concat improvements that are on todo list for 11 which are otherwise very complex and high risk to rework:

JDK-8212726 Replace some use of drop- and foldArguments with filtering argument combinator in StringConcatFactory
JDK-8213035 Pack MethodHandleInlineStrategy coder and length into a long
JDK-8213478 Reduce rebinds when applying repeated filters and conversions
JDK-8222852 Reduce String concat combinator tree shapes by folding constants into prependers
JDK-8223454 Reduce String concatenation shapes by folding initialLengthCoder into last mixer

This is a clean backport.

Testing: x86_64 build, tier1

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Commit messages:
 - Backport b3b41df70fb5ec3187d165786b3c8ad2d4b4012b

Changes: https://git.openjdk.org/jdk11u-dev/pull/2813/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2813&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8212597
  Stats: 107 lines in 3 files changed: 35 ins; 62 del; 10 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2813.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2813/head:pull/2813

PR: https://git.openjdk.org/jdk11u-dev/pull/2813