Improve our own wcwidth implementation and remove dependency on wcwidth package

`TerminalWriter`, imported recently from `py`, contains its own
incomplete wcwidth (`char_with`/`get_line_width`) implementation. The
`TerminalReporter` also needs this, but uses the external `wcwidth`
package.

This commit brings the `TerminalWriter` implementation up-to-par with
`wcwidth`, moves to implementation to a new file `_pytest._io.wcwidth`
which is used everywhere, and removes the dependency.

The differences compared to the `wcwidth` package are:

- Normalizes the string before counting.

- Uses Python's `unicodedata` instead of vendored Unicode tables. This
  means the data corresponds to the Python's version Unicode version
  instead of the `wcwidth`'s package version.

- Apply some optimizations.

testing/io/test_wcwidth.py

@@ -0,0 +1,38 @@
+import pytest
+from _pytest._io.wcwidth import wcswidth
+from _pytest._io.wcwidth import wcwidth
+
+
+@pytest.mark.parametrize(
+    ("c", "expected"),
+    [
+        ("\0", 0),
+        ("\n", -1),
+        ("a", 1),
+        ("1", 1),
+        ("א", 1),
+        ("\u200B", 0),
+        ("\u1ABE", 0),
+        ("\u0591", 0),
+        ("🉐", 2),
+        ("＄", 2),
+    ],
+)
+def test_wcwidth(c: str, expected: int) -> None:
+    assert wcwidth(c) == expected
+
+
+@pytest.mark.parametrize(
+    ("s", "expected"),
+    [
+        ("", 0),
+        ("hello, world!", 13),
+        ("hello, world!\n", -1),
+        ("0123456789", 10),
+        ("שלום, עולם!", 11),
+        ("שְבֻעָיים", 6),
+        ("🉐🉐🉐", 6),
+    ],
+)
+def test_wcswidth(s: str, expected: int) -> None:
+    assert wcswidth(s) == expected