Refactor QGIS 4 patch

[Withalion]

This PR amends the patches done in #4379 to support reading QGIS 4 project files, but use the writing style of QGIS 3. This fixes the issue where users would expect default project from mobile work in QGIS 3.XX and also QGIS 4.XX.

[github-actions]

Pull Request Test Coverage Report for Build 23460529182

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 23 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.1%) to 59.785%

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Files with Coverage Reduction	New Missed Lines	%
mm/app/layerfeaturesmodel.cpp	1	80.47%
mm/core/merginuserauth.cpp	9	68.24%
mm/core/merginapi.cpp	13	75.07%

Totals
Change from base Build 23437519211:	-0.1%
Covered Lines:	8774
Relevant Lines:	14676

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💛 - Coveralls

[github-actions]

📦 Build Artifacts Ready

OS	Status	Build	Info	Workflow run
macOS Build	📬	Mergin Maps 65591 dmg	Expires: 21/06/2026	#6559
linux Build	📬	Mergin Maps 65701 x86_64	Expires: 21/06/2026	#6570
win64 Build	❌	Build failed or not found.		#5754
Android Build	📬	Mergin Maps 787051 APK [arm64-v8a]	Expires: 21/06/2026	#7870
Android Build	📬	Mergin Maps 787011 APK [armeabi-v7a]	Expires: 21/06/2026	#7870
iOS Build	📬		Build number: 26.03.881011	#8810

[github-actions]

📦 Build Artifacts Ready

OS	Status	Build	Info	Workflow run
macOS Build	📬	Mergin Maps 65621 dmg	Expires: 22/06/2026	#6562
linux Build	❌	Build failed or not found.		#6573
win64 Build	❌	Build failed or not found.		#5757
Android Build	📬	Mergin Maps 787351 APK [arm64-v8a]	Expires: 22/06/2026	#7873
Android Build	📬	Mergin Maps 787311 APK [armeabi-v7a]	Expires: 22/06/2026	#7873
iOS Build	📬		Build number: 26.03.881311	#8813