Fix LT-22578: dialog window Z order issues

[thejambi]

Quick Summary

https://jira.sil.org/browse/LT-22578. ShowDialog calls needed to properly pass an owner parameter for the windows to behave as expected. This has been done in #1023 but this did not entirely correct the behavior. The dialog properly had a parent, but while the application was preparing to open the target dialog, another application could temporarily appear on top of the main FieldWorks window. This change fixes behavior so no other application windows get top-level focus before the target dialog is shown.

The issue was reported for "Create new inflectional affix" dialog but I found that this also affected two others, which now also have the shared fix applied. They are:

• Lexicon Edit → Show Subentry under → "..." → Add a Component
• Lexicon Edit → Subentries and/or Referenced Complex Forms → "..." → Add a Complex Form

CI-ready checklist

• Commit messages follow .github/commit-guidelines.md (subject ≤ 72 chars, no trailing punctuation; if body present, blank line then ≤ 80-char lines).
• No whitespace warnings locally:

  git fetch origin
  git log --check --pretty=format:"---% h% s" origin/<base>..
  git diff --check --cached

• Builds/tests pass locally (or I've run the CI-style build via Bash script or MSBuild).
• If this is core-developer AI-assisted work, I followed Docs/workflows/ai-pr-workflow.md and ran pr-preflight or the equivalent branch-readiness review before requesting review.
• For any Src/** folders touched, corresponding AGENTS.md files are updated or explicitly confirmed still accurate.

Notes for reviewers (optional)

---

This change is 

[github-actions]

NUnit Tests

    1 files  ±0      1 suites  ±0   11m 2s ⏱️ -2s
4 320 tests +4  4 247 ✅ +4  73 💤 ±0  0 ❌ ±0 
4 329 runs  +4  4 256 ✅ +4  73 💤 ±0  0 ❌ ±0 

Results for commit 273bfed. ± Comparison against base commit 060a376.

♻️ This comment has been updated with latest results.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 22.22222% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 33.06%. Comparing base (5190c22) to head (273bfed).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ommon/Controls/XMLViews/ReallySimpleListChooser.cs	0.00%	10 Missing and 1 partial ⚠️
.../LexText/Lexicon/EntrySequenceReferenceLauncher.cs	50.00%	2 Missing ⚠️
Src/LexText/Morphology/InflAffixTemplateControl.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1041      +/-   ##
==========================================
+ Coverage   33.05%   33.06%   +0.01%     
==========================================
  Files        1202     1202              
  Lines      278342   278339       -3     
  Branches    37191    37191              
==========================================
+ Hits        91993    92031      +38     
+ Misses     158493   158454      -39     
+ Partials    27856    27854       -2     

Files with missing lines	Coverage Δ
...c/Common/Controls/DetailControls/ChooserCommand.cs	14.86% <100.00%> (+14.86%)	⬆️
Src/Common/Controls/XMLViews/ChooserCommandBase.cs	30.30% <100.00%> (+30.30%)	⬆️
Src/LexText/Morphology/InflAffixTemplateControl.cs	0.00% <0.00%> (ø)
.../LexText/Lexicon/EntrySequenceReferenceLauncher.cs	10.07% <50.00%> (+3.90%)	⬆️
...ommon/Controls/XMLViews/ReallySimpleListChooser.cs	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes

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