RFR: 8266746: C1: Replace UnsafeGetRaw with UnsafeGetObject when setting up OSR entry block

[Yi Yang]

After JDK-8150921, most Unsafe{Get,Put}Raw intrinsic methods can be replaced by Unsafe{Get,Put}Object.

There is the only one occurrence where c1 refers UnsafeGetRaw among GraphBuilder::setup_osr_entry_block()

https://github.com/openjdk/jdk/blob/74fecc070a6462e6a2d061525b53a63de15339f9/src/hotspot/share/c1/c1_GraphBuilder.cpp#L3143-L3157

We can replace UnsafeGetRaw with UnsafeGetObject when setting up OSR entry block. After that, Unsafe{Get,Put}Raw can be completely removed  because no one refers to them.

(This patch actually does two things:
1. `Replace UnsafeGetRaw with UnsafeGetObject when setting up OSR entry block` This is the only occurrence where c1 refers UnsafeGetRaw
2. `Cleanup unused Unsafe{Get,Put}Raw code`
They are related so I put it together, but I still want to hear your suggestions, should they be separated into two patches, or just one patch is enough?)

Thanks!
Yang

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Commit messages:
 - cleanup

Changes: https://git.openjdk.java.net/jdk/pull/3917/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3917&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266746
  Stats: 543 lines in 14 files changed: 23 ins; 514 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3917.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3917/head:pull/3917

PR: https://git.openjdk.java.net/jdk/pull/3917