RFR: 8171508: Remove -Dsun.java.launcher.is_altjvm option [v6]

[Calvin Cheung]

> The `-Dsun.java.launcher.is_altjvm` option is only used in the gtest launcher and has no relationship with the similarly named `-XXaltjvm` option. The gtest launcher also sets the `-XX:+ExecutingUnitTests` option. This RFE involves removing the `-Dsun.java.launcher.is_altjvm` option, capturing the `-XX:+ExecutingUnitTests` option in Arguments::process_sun_java_launcher_properties() so that the os::jvm_path() can check if the option is set before using JAVA_HOME setting.
> 
> Passed tiers 1 - 3 testing.

Calvin Cheung has updated the pull request incrementally with one additional commit since the last revision:

  simplify the code by using stringStream

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24310/files
  - new: https://git.openjdk.org/jdk/pull/24310/files/e107e569..e3ed1a2b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24310&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24310&range=04-05

  Stats: 35 lines in 4 files changed: 6 ins; 12 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/24310.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24310/head:pull/24310

PR: https://git.openjdk.org/jdk/pull/24310