searcher: move "max matches" from printer to searcher

This is a bit of a brutal change, but I believe is necessary in order to
fix a bug in how we handle the "max matches" limit in multi-line mode
while simultaneously handling context lines correctly.

The main problem here is that "max matches" refers to the shorter of
"one match per line" or "a single match." In typical grep, matches
*can't* span multiple lines, so there's never a difference. But in
multi-line mode, they can. So match counts necessarily must be handled
differently for multi-line mode.

The printer was previously responsible for this. But for $reasons, the
printer is fundamentally not in charge of how matches are found and
reported.

See my comments in #3094 for even more context.

This is a breaking change for `grep-printer`.

Fixes #3076, Closes #3094

tests/regression.rs

@@ -1459,6 +1459,7 @@ rgtest!(r2658_null_data_line_regexp, |dir: Dir, mut cmd: TestCommand| {
 rgtest!(r2944_incorrect_bytes_searched, |dir: Dir, mut cmd: TestCommand| {
     dir.create("haystack", "foo1\nfoo2\nfoo3\nfoo4\nfoo5\n");
     let got = cmd.args(&["--stats", "-m2", "foo", "."]).stdout();
+    println!("{got}");
     assert!(got.contains("10 bytes searched\n"));
 });