[foreign-memaccess+abi] RFR: Fix misc typos in FFM API javadoc

[Maurizio Cimadamore]

This PR fixes a bunch of issues found when running grammar code inspection in IntelliJ.

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Commit messages:
 - Initial push

Changes: https://git.openjdk.org/panama-foreign/pull/873/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=873&range=00
  Stats: 7 lines in 2 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/873.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign.git pull/873/head:pull/873

PR: https://git.openjdk.org/panama-foreign/pull/873