RFR: 8368573: MultiBranchNode::required_outcnt should return an unsigned int

[Manuel Hässig]

This small PR turns the type `MultiBranchNode::required_outcnt` from an `int` into a `uint` because all usages of this are already unsigned integers. Thus, the patch eliminates all implicit conversion from the code path.

Testing:
 - [ ] Github Actions
 - [x] tier1, tier2 on Oracle supported platforms

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Commit messages:
 - Make MultiBranchNode::required_outcnt unsigned

Changes: https://git.openjdk.org/jdk/pull/27714/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27714&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368573
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/27714.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27714/head:pull/27714

PR: https://git.openjdk.org/jdk/pull/27714