RFR: 8368681: Shenandoah: Add documentation comments for ShenandoahAllocationRate [v2]

[Kelvin Nilsen]

> Add documentation to ShenandoahAllocationRate

Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:

  Fix several typos

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27505/files
  - new: https://git.openjdk.org/jdk/pull/27505/files/2dce29d2..35bce7e3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27505&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27505&range=00-01

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/27505.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27505/head:pull/27505

PR: https://git.openjdk.org/jdk/pull/27505