RFR: 8359437: Make users and test suite not able to set LockingMode flag [v2]

[Anton Artemov]

> This PR contains changes for the 1st phase of the `LockingMode` flag obsoletion. 
> 
> The work is done by @fbredber, I have taken it over and am finishing it while he's on vacation. 
> 
> In the 1st phase one keeps the `LockingMode` variable in all places, but makes it non-settable from the command line. All the C1 and C2 code related to legacy locking will still be in place (but as dead code) and removed later (phase 2).
> 
> Lightweight locking is the default locking from now on.
> 
> Tested in tiers 1 - 7.

Anton Artemov has updated the pull request incrementally with two additional commits since the last revision:

 - 8359437: Addressed reviewers' comments
 - 8359437: Addressed reviewers' comments

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/25847/files
  - new: https://git.openjdk.org/jdk/pull/25847/files/30de697d..215ee92d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25847&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25847&range=00-01

  Stats: 39 lines in 8 files changed: 0 ins; 38 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25847.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25847/head:pull/25847

PR: https://git.openjdk.org/jdk/pull/25847