fix(files): conversion api simplification and conflict check

[skjnldsv]

Followup #49922

• Simplified the Conversion provider supported mime declaration
• Added extension information
• Restructured a bit the manager
• Automatically detect file conflicts and adjust accordingly
• Tests

[juliusknorr]

Code looks good and works as expected now with and without passing a destination to the OCS endpoint

[provokateurin]

IMO the translations should omit the extension, as we can build this string ourselves using the provided extension.

[skjnldsv]

I thought about this, I don't know how flexible we want to make it.
Do we ALWAYS want to show the (.png) part ?

cc @marcoambrosini @nimishavijay
for context, this would be visible in the Save as submenu,

Entries would be like this

• Image (.jpg)
• Image (.png)
• Image (.gif)

Maybe we should directly use more human text like this? Then we can omit the extension alltogether?

• Jpeg image
• Png image
• Gif image

[provokateurin]

True, for example Windows doesn't even display the file extensions anymore, so they could be meaningless to many users.

[marcoambrosini]

From my perspective It makes little difference and I'd be fine with both approaches

[skjnldsv]

@provokateurin maybe we can tackle the l10n on a followup once we have an answer from the design team? :)

[provokateurin]

Code looks good, but unfortunately you need to fix the depencencies 🙈