RFR: 8294087: RISC-V: RVC: Fix a potential alignment issue and add more alignment assertions for the patchable calls/nops [v4]

[Xiaolin Zheng]

> With RVC turning on, we must carefully keep all runtime-patchable instructions aligned. Code is running at full speed, when patching unaligned instructions spanning cache lines, concurrency issues may occur. This patch fixes a potential alignment issue of the patchable nop after MachUEPNode, with adding some strong alignment assertions as well. (In fact, currently the `nop` in the Verified Entry Point is fortunately aligned to 4 under RVC even without this patch, so this patch doesn't change program behaviors.)
> 
> Tested hotspot tier1 and tier2 together with other patches on QEMU.

Xiaolin Zheng has updated the pull request incrementally with two additional commits since the last revision:

 - Modifications as review comments again
 - Revert "(Revertible) Just to see which code style is better"
   
   This reverts commit 229d535e93ceeff4f6ba32a2c882599e2999999b.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/10370/files
  - new: https://git.openjdk.org/jdk/pull/10370/files/229d535e..8ab3377d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10370&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10370&range=02-03

  Stats: 14 lines in 9 files changed: 1 ins; 2 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/10370.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10370/head:pull/10370

PR: https://git.openjdk.org/jdk/pull/10370