bzegrep, bzfgrep, rgrep, zegrep, zgrep: move from linux to common (#8709)

grep alternatives work substantially the same on all major platforms.

pages/common/rgrep.md

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+# rgrep
+
+> Recursively find patterns in files using regular expressions.
+> Equivalent to `grep -r`.
+> More information: <https://www.gnu.org/software/grep/manual/grep.html>.
+
+- Recursively search for a pattern in the current working directory:
+
+`rgrep "{{search_pattern}}"`
+
+- Recursively search for a case-insensitive pattern in the current working directory:
+
+`rgrep --ignore-case "{{search_pattern}}"`
+
+- Recursively search for an extended regular expression pattern (supports `?`, `+`, `{}`, `()` and `|`) in the current working directory:
+
+`rgrep --extended-regexp "{{search_pattern}}"`
+
+- Recursively search for an exact string (disables regular expressions) in the current working directory:
+
+`rgrep --fixed-strings "{{exact_string}}"`
+
+- Recursively search for a pattern in a specified directory (or file):
+
+`rgrep "{{search_pattern}}" {{path/to/file_or_directory}}`