RFR: 8354871: Replace stack map frame type magics with constants

[Francesco Andreuzzi]

In this PR I introduce some constants in `StackMapGenerator`. No change in logic is expected.

Passes tests in `jdk/classfile`.

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Commit messages:
 - nn
 - Merge branch 'master' into JDK-8354871
 - constants

Changes: https://git.openjdk.org/jdk/pull/27029/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27029&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8354871
  Stats: 124 lines in 7 files changed: 21 ins; 26 del; 77 mod
  Patch: https://git.openjdk.org/jdk/pull/27029.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27029/head:pull/27029

PR: https://git.openjdk.org/jdk/pull/27029