RFR: 8269736: Optimize CDS PatchEmbeddedPointers::do_bit() [v3]

[Matias Saavedra Silva]

> The current implementation reads the narrow oop, decodes it using the "dump time" encoding, encodes it using "runtime" encoding, and then stores it back into the heap. In the cases where the dumptime and runtime shifts are equal, there is an opportunity to calculate the fixed distance between oops so they can be patched more optimally. Verified with tier 1, 2, and 4 tests.

Matias Saavedra Silva has updated the pull request incrementally with two additional commits since the last revision:

 - Ashutosh comments
 - Fixed minimal and cross build

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10863/files
  - new: https://git.openjdk.org/jdk/pull/10863/files/6741a6df..5b9f2e1d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10863&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10863&range=01-02

  Stats: 17 lines in 2 files changed: 6 ins; 7 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/10863.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10863/head:pull/10863

PR: https://git.openjdk.org/jdk/pull/10863