[code-reflection] RFR: Model verifier

[Adam Sotona]

This patch starts work on model `Verifier` and implements following verifications:
 - operands declaration dominance
 - `BranchOp` reference arguments matching target block parameters (simple matching by `TypeKind` with erased `int` sub-types)
 - `ArithmeticOperation`, `TestOperation` and `ConvOp` verified presence of relevant method handler in `InvokableLeafOps`
 
`TestSmallCorpus` is improved to verify code model.

Fixes of bugs newly discovered by the `TestSmallCorpus`:
 - missing methods in `InvokableLeafOps`
 - `Interpreter` use of provided lookup for `resolveToMethodType`
 - `Interpreter` erase  sub-`int` types for `InvokeOp` execution + added `TestLiftCustomBytecode::testEraseInts`
-  Removed complex sub-`int` types calculation from `BytecodeLift` and `LocalsToVarMapper` 
- `BytecodeLift` fixed to avoid production of some obsolete block parameters

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Commit messages:
 - Interpreter erase int types + added TestLiftCustomBytecode::testEraseInts
 - relaxed verification of block parameters
 - reversion of NullTypeResolver
 - NullTypeResolver work in progress
 - removed unused imports
 - fixed merge of boolean segments in LocalsToVarMapper
 - Verifier work in progress
 - intermediate NULL_TYPE is resolved as post-lift transformation
 - Draft of post-lift transform pulling null ConstantOp type from its uses
 - Verifier work in progress
 - ... and 10 more: https://git.openjdk.org/babylon/compare/cfffc996...104ef7dd

Changes: https://git.openjdk.org/babylon/pull/247/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=247&range=00
  Stats: 425 lines in 7 files changed: 314 ins; 60 del; 51 mod
  Patch: https://git.openjdk.org/babylon/pull/247.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/247/head:pull/247

PR: https://git.openjdk.org/babylon/pull/247