fix: prevent drop files overlay from appearing when dragging text

[oscar-escire]

References

• Fixes Dragging text selection over submission form triggers "drop files" message #1268
• Port of [Port dspace-7_x] fix: prevent drop files overlay from appearing when dragging text #5164

Description

Prevent the "drop files" overlay from appearing when dragging text selections in Firefox on submission pages.

List of changes in this PR:

• Added dataTransfer.types.includes('Files') guard in UploaderComponent.onDragOver() (uploader.component.ts)
• Added the same guard in FileDropzoneNoUploaderComponent.onDragOver() (file-dropzone-no-uploader.component.ts)

Instructions for Reviewers

1. Open the application in Firefox
2. Navigate to a new submission or edit a workspace item
3. Select some text on the page
4. Drag the text selection around the page
5. Expected: The "Drop files" overlay should NOT appear
6. Now drag an actual file from your file explorer onto the page
7. Expected: The "Drop files" overlay should appear as normal

Checklist

• My PR is created against the main branch of code (unless it is a backport or is fixing an issue specific to an older branch).
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