[code-reflection] RFR: Switch lowering fixes [v2]

[Adam Sotona]

> This patch fixes `bytecode/impl/LoweringTransform` with unboxing selector, implicit default target leading to exit block and conversion of constant labels.
> Unreflect runs of `TestSwitchExpressionOp` and `TestSwitchStatementOp` are now enabled and pass.

Adam Sotona has updated the pull request incrementally with one additional commit since the last revision:

  fixed ConstantLabelSwitchOp javadoc and Character unboxing

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Changes:
  - all: https://git.openjdk.org/babylon/pull/804/files
  - new: https://git.openjdk.org/babylon/pull/804/files/d74dd1da..27e06948

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=babylon&pr=804&range=01
 - incr: https://webrevs.openjdk.org/?repo=babylon&pr=804&range=00-01

  Stats: 7 lines in 2 files changed: 4 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/babylon/pull/804.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/804/head:pull/804

PR: https://git.openjdk.org/babylon/pull/804