RFR: 8267956: C1 code cleanup

[Yi Yang]

While skimming C1 code, I found a lot of useless/invalid/unimplemented code, they can be harmless removed.

- Unused IntInterval in type hierarchy
- Unused MethodDataConstant in type hierarchy
- Unused MethodDataType in type hierarchy
- Unused LIRGenerator::maybe_mask_boolean after JDK-XXX...
- Unused is_*_stub() **virtual methods** in CodeStub
- Unused start_block and bind_block_entry declarations in c1_LIRGenerator.hpp
- Residual do_ClassIDIntrinsic declarations in c1_LIRGenerator.hpp
- Meet/join are never implemented
- LIRTracePeephole does nothing, also its name is confusing
- Directly define inline functions in c1_ValueSet.hpp and remove c1_ValueSet.inline.hpp and c1_ValueSet.cpp files
- Duplicated Compilation::count_invocations() and Compilation::count_backedges()
- Remove c1_Defs.cpp
- Remove lir_backwardbranch_target

Thanks!

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Commit messages:
 - c1 code cleanup

Changes: https://git.openjdk.java.net/jdk/pull/4508/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4508&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267956
  Stats: 241 lines in 18 files changed: 5 ins; 217 del; 19 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4508.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4508/head:pull/4508

PR: https://git.openjdk.java.net/jdk/pull/4508