RFR: 8336777: BufferedMethodBuilder not initialized with static flag

[Chen Liang]

`BufferedMethodBuilder` accepts a static flag and passes it to the `CodeBuilder` it creates; yet it does not prevent static flag tampering like `DirectMethodBuilder` does. This patch makes their behaviors consistent.

Note that the throwing of IAE is provisional; it is open to discussion later.

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Commit messages:
 - 8336777: BufferedMethodBuilder not initialized with static flag

Changes: https://git.openjdk.org/jdk/pull/20244/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20244&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336777
  Stats: 102 lines in 6 files changed: 91 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/20244.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20244/head:pull/20244

PR: https://git.openjdk.org/jdk/pull/20244