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.

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/std/debug.zig b/lib/std/debug.zig
index 907f7711a7..6d034146c3 100644
--- a/lib/std/debug.zig
+++ b/lib/std/debug.zig
@@ -27,6 +27,12 @@ pub const SourceLocation = struct {
     line: u64,
     column: u64,
     file_name: []const u8,
+
+    pub const invalid: SourceLocation = .{
+        .line = 0,
+        .column = 0,
+        .file_name = &.{},
+    };
 };
 
 pub const Symbol = struct {