tooltip: Download tooltip on file.

[isakhagg]

Fixes #19740

Testing plan:
Visualtesting and automatic tests.

GIFs or screenshots:

[isakhagg]

@alexmv or @timabbott Could you have a look at this PR? It fixes issue #19740

[timabbott]

This is great @isakhagg! I merged this after a few minor changes:

• Adjusted the commit message to close Show "Download <filename>..." tooltip on uploaded file links #19740.
• Added a comment explaining the motivation for this block of code.
• Renamed the variable in the string from variable to filename, since that's more naturally helpful, both for reading the code and for the dozens of translators who will end up translating this string into their language.