RFR: 8339519: Remove size field from instructions

[Chen Liang]

`AbstractInstruction` has a redundant `size` field unnecessary for the majority of instructions. We should add this field to the 2 switch instructions that need it only.

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Commit messages:
 - 8339519: Remove size field from instructions

Changes: https://git.openjdk.org/jdk/pull/20880/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20880&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339519
  Stats: 73 lines in 1 file changed: 8 ins; 12 del; 53 mod
  Patch: https://git.openjdk.org/jdk/pull/20880.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20880/head:pull/20880

PR: https://git.openjdk.org/jdk/pull/20880