Try to stop users from cloning instances into themselves

[HebaruSan]

Motivation

If a user clones a game instance into a subfolder of itself, the copy goes on forever and eventually fills the disk if not stopped.

Changes

Now when you clone an instance, we check whether any of the parent folders of the destination are the same as the source, and if so we emit an error and abort the clone.
A test is included to exercise this.

Fixes #4520.

Known limitations

Note that catching all ways to try to copy a directory into itself is a well-known impossible task, because different paths can point to the same location in obfuscated ways:

• Make a junction / symbolic link to the game instance, then clone from the original folder into the symbolic link
• Mount a network share at one drive letter and a subfolder of it at another drive letter, then clone from one drive to the other
• And so on for any OS capability to assign arbitrary names to paths

While we can't detect everything, catching the very simplest case where everything is a normal directory is still easy enough to be worth it.

[coveralls]

Coverage Report for CI Build 24295459733

Coverage increased (+0.04%) to 85.543%

Details

• Coverage increased (+0.04%) from the base build.
• Patch coverage: 6 of 6 lines across 2 files are fully covered (100%).
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	14223
Covered Lines:	12013
Line Coverage:	84.46%
Relevant Branches:	2164
Covered Branches:	2005
Branch Coverage:	92.65%
Branches in Coverage %:	Yes
Coverage Strength:	1.76 hits per line

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💛 - Coveralls