Don't drop dot-entries for patterns with a literal leading dot

[jaideeppyne]

glob_with returns nothing for patterns like .git* when require_literal_leading_dot is set, even though .gitignore is sitting right there.

fill_todo drops every directory entry whose name starts with a . before the entry is ever matched against the pattern for that component. But require_literal_leading_dot only asks that the . appear literally in the pattern — and in .git* it does. Pattern::matches_with gets this right (test_pattern_matches_require_literal_leading_dot already covers aaa/bbb/.* vs aaa/bbb/.ccc), so the two APIs disagree about the same component:

// .gitignore exists in the current directory
let opts = MatchOptions { require_literal_leading_dot: true, ..MatchOptions::new() };
Pattern::new(".git*").unwrap().matches_with(".gitignore", opts); // true
glob_with(".git*", opts).unwrap().count();                       // 0

fnmatch(".git*", ".gitignore", FNM_PERIOD) and the shell both match, so Pattern is the one that's right here.

The filter still has a job to do: a recursive ** component matches directory entries without consulting the pattern at all, which is what #128 fixed for #67. So I kept it for every pattern that doesn't start with a literal .. A ** component always parses to a single AnyRecursiveSequence token, so it can never take the new exemption and #67 stays fixed. The predicate is the same one that already guards the . and .. special entries a few lines below, so I hoisted it into a local.

Tests in tests/glob-std.rs cover .a*, .?aa and .[ab]bb matching hidden entries, plus * and ?aa still skipping them. I checked the results against bash on a dot-heavy tree for around 20 patterns and they agree.

I left the .to_str().unwrap() on that line alone since #162 is already dealing with it.

Disclosure: this change was written with AI assistance. The bug was found by differential-testing against fnmatch(3) and bash; I reviewed the diff and reproduced both the bug and the fix locally.