Rename `Condition` into `SystemCondition`

[Shatur]

What problem does this solve or what need does it fill?

The current Condition trait name is overly generic and appears in the prelude.

What solution would you like?

Since users rarely type this trait directly, I suggest renaming it to something more specific like SystemCondition or SystemOperator.

Use case

In bevy_replicon, I wanted to provide a concise Condition enum for replication rules. The current naming collision forces me to choose a less ergonomic name, despite this being a type users will reference frequently.

[benfrankel]

Another solution would be to remove the name from the prelude while still re-exporting the trait itself, as suggested in #13959, although that was closed as not planned.