fossil*: move all fossil commands to common vs linux (#8677)

fossil commands work substantially the same on all major platforms.

pages/common/fossil.md

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+# fossil
+
+> Distributed version control system.
+> Some subcommands such as `fossil commit` have their own usage documentation.
+> More information: <https://fossil-scm.org/>.
+
+- Check the Fossil version:
+
+`fossil version`
+
+- Show general help (list available subcommands):
+
+`fossil help`
+
+- Show help on a Fossil subcommand (like `add`, `commit`, etc.):
+
+`fossil help {{subcommand}}`
+
+- Execute a Fossil subcommand:
+
+`fossil {{subcommand}}`