Move IO#readline to Ruby

This commit moves IO#readline to Ruby.  In order to call C functions,
keyword arguments must be converted to hashes.  Prior to this commit,
code like `io.readline(chomp: true)` would allocate a hash.  This
commits moves the keyword "denaturing" to Ruby, allowing us to send
positional arguments to the C API and avoiding the hash allocation.

Here is an allocation benchmark for the method:

```
x = GC.stat(:total_allocated_objects)
File.open("/usr/share/dict/words") do |f|
  f.readline(chomp: true) until f.eof?
end
p ALLOCATIONS: GC.stat(:total_allocated_objects) - x
```

Before this commit, the output was this:

```
$ make run
./miniruby -I./lib -I. -I.ext/common  -r./arm64-darwin22-fake  ./test.rb
{:ALLOCATIONS=>707939}
```

Now it is this:

```
$ make run
./miniruby -I./lib -I. -I.ext/common  -r./arm64-darwin22-fake  ./test.rb
{:ALLOCATIONS=>471962}
```

[Bug #19890] [ruby-core:114803]

1 files changed, 13 insertions, 0 deletions

diff --git a/io.rb b/io.rb
index 40873ea4fd..549c5e62bd 100644
--- a/io.rb
+++ b/io.rb
@@ -120,4 +120,17 @@ class IO
   def write_nonblock(buf, exception: true)
     Primitive.io_write_nonblock(buf, exception)
   end
+
+  # call-seq:
+  #   readline(sep = $/, chomp: false)   -> string
+  #   readline(limit, chomp: false)      -> string
+  #   readline(sep, limit, chomp: false) -> string
+  #
+  # Reads a line as with IO#gets, but raises EOFError if already at end-of-stream.
+  #
+  # Optional keyword argument +chomp+ specifies whether line separators
+  # are to be omitted.
+  def readline(sep = $/, limit = nil, chomp: false)
+    Primitive.io_readline(sep, limit, chomp)
+  end
 end