Login and Registration: Add a "Show password" button on the login page.

The ability for users to see the password they're typing improves usability and accessibility of the login users flow.

- brings the login screen in line with the same feature already used in the New User, Edit User, and Reset Password pages
- improves association of labels and input fields by using explicit association with `for` / `id` attributes
- slightly increases the "Remember me" label font size

Props johnbillion, Iceable, audrasjb, joyously, adamsilverstein, boemedia, DrewAPicture, shadyvb, birgire, peterwilsoncc, pento, anevins, davidbaumwald, whyisjake, afercia.
Fixes #42888.

Built from https://develop.svn.wordpress.org/trunk@46256


git-svn-id: http://core.svn.wordpress.org/trunk@46068 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/install.css

@@ -301,6 +301,17 @@ body.rtl,
 		box-sizing: border-box;
 	}
 
+	.wp-pwd #pass1 {
+		padding-right: 50px;
+	}
+
+	.wp-pwd .button.wp-hide-pw {
+		right: 0;
+	}
+
+	#pass-strength-result {
+		width: 100%;
+	}
 }
 
 body.language-chooser {