code coverage dumping tool basic implementation

* std.debug.Dwarf: add `sortCompileUnits` along with a field to track
  the state for the purpose of assertions and correct API usage.
  This makes batch lookups faster.
  - in the future, findCompileUnit should be enhanced to rely on sorted
    compile units as well.
* implement `std.debug.Dwarf.resolveSourceLocations` as well as
  `std.debug.Info.resolveSourceLocations`. It's still pretty slow, since
  it calls getLineNumberInfo for each array element, repeating a lot of
  work unnecessarily.
* integrate these APIs with `std.Progress` to understand what is taking
  so long.

The output I'm seeing from this tool shows a lot of missing source
locations. In particular, the main area of interest is missing for my
tokenizer fuzzing example.

tools/dump-cov.zig

@@ -28,7 +28,10 @@ pub fn main() !void {
         .sub_path = cov_file_name,
     };
 
-    var debug_info = std.debug.Info.load(gpa, exe_path) catch |err| {
+    const prog_node = std.Progress.start(.{});
+    defer prog_node.end();
+
+    var debug_info = std.debug.Info.load(gpa, exe_path, prog_node) catch |err| {
         fatal("failed to load debug info for {}: {s}", .{ exe_path, @errorName(err) });
     };
     defer debug_info.deinit(gpa);
@@ -51,7 +54,10 @@ pub fn main() !void {
     assert(std.sort.isSorted(usize, pcs, {}, std.sort.asc(usize)));
 
     const source_locations = try arena.alloc(std.debug.SourceLocation, pcs.len);
-    try debug_info.resolveSourceLocations(gpa, pcs, source_locations);
+    try debug_info.resolveSourceLocations(gpa, pcs, source_locations, prog_node);
+    defer for (source_locations) |sl| {
+        gpa.free(sl.file_name);
+    };
 
     for (pcs, source_locations) |pc, sl| {
         try stdout.print("{x}: {s}:{d}:{d}\n", .{