RFR: JDK-8301460: Clean up LambdaForm to reference BasicType enums directly [v2]

[Mandy Chung]

> `LambdaForm` declares int constants for `BasicType::ordinal` to workaround JDK-8161245.   Now these int constants are no longer needed.    This removes these int constants and reference `BasicType` enums directly.

Mandy Chung has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' of https://github.com/openjdk/jdk into JDK-8301460
 - further clean up
 - JDK-8301460: Code in LambdaForm.java still refers to resolved JDK-8161245

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12546/files
  - new: https://git.openjdk.org/jdk/pull/12546/files/029effa0..75f07dea

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12546&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12546&range=00-01

  Stats: 57732 lines in 1241 files changed: 24871 ins; 16438 del; 16423 mod
  Patch: https://git.openjdk.org/jdk/pull/12546.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12546/head:pull/12546

PR: https://git.openjdk.org/jdk/pull/12546