fix: Route file writing through FileSystem

[bitsandfoxes]

Fixes #3607, getsentry/sentry-unity#1804

Problem

Writing to disk is restricted on platforms like the Switch, causing crashes. There's currently no way to properly opt-out of this. I.e. the SDK creates and tries to persist an ID to disk out-of-the-box.

Solution

• Adding a new flag to the options: DisableFileWrite.
• We've already got IFileSystem in place. Making sure to make it is respecting that flag
• Find all write instances, i.e. File.Create and Directory.Create and replace them with IFileSystem.
• Tests

TODO

• Add automatic detection/linting of any use of create, move, and delete` to prevent regressions

[bruno-garcia]

Just realize the strategy with returning bool has an issue. since the caller doesn't know if it failed, or if it's an option picked by the user and will log a bunch of error with the sdk debug logger

You might not be able to hide that all in the file writer abstraction, leaving the knowledge of the option to the callsites and hence skipping the operation altogether.

Or change the interface to return some enum where it can be failure or disabled. Or return null boolean to be simple. and document that null means disable and true/false is the real output

[bitsandfoxes]

I'd like to keep the DisableFileWrite check in one place if possible. I think it's going to be much easier to maintain instead of having to check for it in every place the SDK is attempting to write something to disk.
The "failure to write" should be handled regardless of reason by the caller. But I'm adding the null as return value to allow for a more granular handling, i.e. retry or somesuch.

[jamescrosswell]

LGTM

[bruno-garcia]

this couldn’t have using anymore? I’m concerned an exception will keep dangling filesa