Upgrade/Install: Bring some consistency to installation screen styles.

* Include `forms.css` and `l10n.css`, for consistency with login screen and other admin screens.
* Remove redundant `@import` directives from `login.css` for files already declared as dependencies.
* Adjust margin on password strength meter for consistency with other fields.
* Increase font size for "You will need this password to log in" notice.
* Fix misaligned icon on "Hide" button for the password.

Props iseulde, dan@micamedia.com, bassgang, cdog, johnbillion, nmenescardi, mukesh27, SergeyBiryukov.
Fixes #35776, #47757, #47758.
Built from https://develop.svn.wordpress.org/trunk@45673


git-svn-id: http://core.svn.wordpress.org/trunk@45484 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/forms-rtl.css

@@ -464,7 +464,7 @@ fieldset label,
 	background-color: #eee;
 	border: 1px solid #ddd;
 	color: #23282d;
-	margin: -1px 0 5px;
+	margin: -1px 1px 5px;
 	padding: 3px 5px;
 	text-align: center;
 	width: 25em;
@@ -522,7 +522,7 @@ fieldset label,
 
 .wp-pwd [type="text"],
 .wp-pwd [type="password"] {
-	margin: 0;
+	margin-bottom: 0;
 	/* Same height as the buttons */
 	line-height: 20px;
 	min-height: 28px;
@@ -542,10 +542,6 @@ fieldset label,
 	display: inline-block;
 }
 
-.form-table span.description.important {
-	font-size: 12px;
-}
-
 p.search-box {
 	float: left;
 	margin: 0;