#2102 set ideRoot during msi installation correctly

[quando632]

This PR fixes #2102

Implemented changes:

• AbstractIdeContext: ideRoot is no longer final; added setIdeRoot(Path) so the context can
  reflect the derived install target.
• IdeContext: added setIdeRoot(Path) to the interface.
• IdeasyCommandlet.installIdeasy(...): after deriving the target via determineIdeRoot(cwd), it
  now calls context.setIdeRoot(...), keeping the whole install run consistent.
• AbstractIdeTestContext: removed the now-redundant ideRoot/ideRootSet fields and
  getIdeRoot/setIdeRoot overrides the test context inherits the production setter, aligning
  test and production behaviour.
• Added test IdeasyCommandletTest#testInstallIdeasyUpdatesIdeRoot (windows/mac/linux) that fails
  without the fix and passes with it.

Verified the invariants called out in the issue are unaffected: the isIdeRootRequired gate in
applyAndRun, and the temp-download-path creation guarded by ideRoot != null in the constructor.

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Testing instructions

1. Automated: in cli/, run mvn -Dtest=IdeasyCommandletTest test all cases pass, including
   the new testInstallIdeasyUpdatesIdeRoot. (Reverting the context.setIdeRoot(...) line makes the
   3 new cases fail, confirming the test reproduces the bug.)

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Checklist for this PR

Make sure everything is checked before merging this PR. For further info please also see
our DoD.

• When running mvn clean test locally all tests pass and build is successful
• PR title is of the form #«issue-id»: «brief summary» (e.g. #921: fixed setup.bat). If no issue ID exists, title only.
• PR top-level comment summarizes what has been done and contains link to addressed issue(s)
• PR and issue(s) have suitable labels
• Issue is set to In Progress and assigned to you or there is no issue (might happen for very small PRs)
• You followed all coding conventions
• You have added the issue implemented by your PR in CHANGELOG.adoc unless issue is labeled with internal
• You have formulated clear instructions on how to test your contribution under "Testing instructions"

[coveralls]

Coverage Report for CI Build 29415537689

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Coverage: 72.281%

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Coverage Stats

Relevant Lines:	16736
Covered Lines:	12603
Line Coverage:	75.3%
Relevant Branches:	7464
Covered Branches:	4889
Branch Coverage:	65.5%
Branches in Coverage %:	Yes
Coverage Strength:	3.19 hits per line

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💛 - Coveralls

[oanding-blrng]

The provided testing instructions are working as expected, other tests are running successfully. I added four suggestion as part of my review.

Also, in case, that the behaviour mentioned in ticket #2102 negatively impacts the user, the testing instructions should be extended to include proper instructions for manually testing correct behaivour.

[quando632]

So, the issue does not negatively impact the user. At its core, it is a robustness and root-cause fix. The only actual user-visible symptom was issue #1517

[oanding-blrng]

So, the issue does not negatively impact the user. At its core, it is a robustness and root-cause fix. The only actual user-visible symptom was issue #1517

Then the current testing instructions are fine. This ticket can move forward.