Replace deprecated ProgressDialog with modern AlertDialog

[Roniscend]

Description (required)
Replacing all deprecated instances of android.app.ProgressDialog across the app with a modern AlertDialog
Fixes #3487

Tests performed (required)

Tested on Pixel 9 6.5.0-debug (Android16)

[Copilot]

Pull request overview

This PR replaces deprecated android.app.ProgressDialog usages with a custom progress UI built on androidx.appcompat.app.AlertDialog, aligning the app with modern Android APIs and addressing #3487.

Changes:

• Added a reusable DialogUtil.createProgressDialog(...) helper that shows an indeterminate ProgressBar with a message.
• Migrated multiple Activities/Fragments from ProgressDialog to the new AlertDialog-based progress dialog.
• Introduced a new localized string for “Saving in progress…” and wired it into Nearby export flows.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
app/src/main/res/values/strings.xml	Adds saving_in_progress string used by Nearby export progress UI.
app/src/main/java/fr/free/nrw/commons/utils/ImageUtils.kt	Replaces avatar progress ProgressDialog with AlertDialog created via DialogUtil.
app/src/main/java/fr/free/nrw/commons/utils/DialogUtil.kt	Adds createProgressDialog(...) helper building an AppCompat AlertDialog with a ProgressBar.
app/src/main/java/fr/free/nrw/commons/upload/depicts/DepictsFragment.kt	Replaces depicts progress ProgressDialog with new DialogUtil progress dialog.
app/src/main/java/fr/free/nrw/commons/upload/categories/UploadCategoriesFragment.kt	Replaces categories progress ProgressDialog with new DialogUtil progress dialog.
app/src/main/java/fr/free/nrw/commons/upload/UploadActivity.kt	Replaces upload progress ProgressDialog initialization with new DialogUtil progress dialog.
app/src/main/java/fr/free/nrw/commons/nearby/fragments/NearbyParentFragment.kt	Uses new DialogUtil progress dialog during GPX/KML export.
app/src/main/java/fr/free/nrw/commons/description/DescriptionEditActivity.kt	Replaces caption/description update ProgressDialog with new DialogUtil progress dialog.
app/src/main/java/fr/free/nrw/commons/auth/LoginActivity.kt	Replaces login ProgressDialog with new DialogUtil progress dialog.

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[github-actions]

✅ Generated APK variants!

• 🤖 Download prodDebugAPK
• 🤖 Download betaDebugAPK

[Roniscend]

@nicolas-raoul can you review this pr also apologies for accidentally closing and reopening this pull request while managing multiple branches in my fork.

[chrisdebian]

Checked the showSettingWallpaperProgressBar removal specifically since it looked like it might drop a feature — confirmed it has no call sites even on current main, so this is dead-code cleanup, not a regression. One small leftover: ImageUtilsTest.kt still has an unused @Mock progressDialogWallpaper: AlertDialog — harmless, but could be removed since the production dialog it mocked no longer exists.