[foreign-memaccess+abi] RFR: added get/set-AtIndex methods for byte, boolean

[RedIODev]

This PR adds the left out getAtIndex and setAtIndex methods for byte and boolean to java.lang.foreign.MemorySegment.java

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Commit messages:
 - added get/set-AtIndex methods for byte, boolean

Changes: https://git.openjdk.org/panama-foreign/pull/747/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=747&range=00
  Stats: 98 lines in 1 file changed: 98 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/747.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/747/head:pull/747

PR: https://git.openjdk.org/panama-foreign/pull/747