Add --less-search-pattern option to tell less to search for pattern

The `less` pager can search for a pattern. In addition, you can instruct it to
search for a given pattern on startup by passing in the `-p` flag followed by
the pattern to search for. Since the `batgrep` command is searching for a
pattern and invoking the pager, it has the opportunity to take advantage of this
functionality.

This patch adds a `-p` flag to `batgrep` which, in turn, passes `-p $PATTERN` to
the pager invoked. This may be specific to `less`, which is
unfortunate. However, it doesn't seem like there would be a convenient way to
make this more general. In addition, most pagers forward the actual paging to
`less` anyways.

To clarify that the behavior is specific to `less`, the long name is
`--less-search-pattern`.

src/batgrep.sh

@@ -30,6 +30,7 @@ OPT_CONTEXT_AFTER=2
 OPT_FOLLOW=true
 OPT_SNIP=""
 OPT_HIGHLIGHT=true
+OPT_SEARCH_PATTERN=false
 BAT_STYLE="header,numbers"
 
 # Set options based on the bat version.
@@ -76,6 +77,8 @@ while shiftopt; do
 		--no-follow)                   OPT_FOLLOW=false;;
 		--no-snip)                     OPT_SNIP="";;
 		--no-highlight)                OPT_HIGHLIGHT=false;;
+		-p|--less-search-pattern)      OPT_LESS_SEARCH_PATTERN=true;;
+		--no-search-pattern)           OPT_SEARCH_PATTERN=false;;
 
 		# Option Forwarding
 		--rg:*) {
@@ -134,6 +137,10 @@ if [[ "$OPT_CONTEXT_BEFORE" -eq 0 && "$OPT_CONTEXT_AFTER" -eq 0 ]]; then
 	OPT_HIGHLIGHT=false
 fi
 
+if [[ "$OPT_LESS_SEARCH_PATTERN" = true ]]; then
+    SCRIPT_PAGER_ARGS+=(-p "$PATTERN")
+fi
+
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 # Main:
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