RTL CSS generation: Switch from CSSJanus to RTLCSS.

CSSJanus (introduced in [26107]), we had a great time with you, but sadly you don't like our fancy CSS.

RTLCSS is a framework for converting CSS from LTR to RTL, same as CSSJanus, with support for more CSS properties like `transform`, `transition` or multiple box and text shadows.

Changes:
* devDependencies: Remove `grunt-cssjanus`, add `grunt-rtlcss`.
* RTLCSS uses `/* rtl:ignore */` to ignore a rule, switch existing `/* @noflip */` to the new directive.
* RTLCSS supports the `transform` property, means we can remove some ignore rules.
* RTLCSS supports string maps for custom replace rules. This commit includes a rule `import-rtl-stylesheet` which replaces ".css" with "-rtl.css" in URLs.

Notes for core development:
* The file generation task is still `grunt rtl`.
* If you have used `grunt cssjanus` before, use `grunt rtlcss` now.
* Remember the new directive `/* rtl:ignore */`.

fixes #31332.

Build: https://build.trac.wordpress.org/changeset/31554
Built from https://develop.svn.wordpress.org/trunk@31573


git-svn-id: http://core.svn.wordpress.org/trunk@31554 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/css/jquery-ui-dialog.css

@@ -128,7 +128,7 @@
 	bottom: -5px;
 	left: 0;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-e {
 	cursor: e-resize;
 	width: 7px;
@@ -136,7 +136,7 @@
 	top: 0;
 	height: 100%;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-w {
 	cursor: w-resize;
 	width: 7px;
@@ -144,7 +144,7 @@
 	top: 0;
 	height: 100%;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-se {
 	cursor: se-resize;
 	width: 12px;
@@ -152,7 +152,7 @@
 	right: 1px;
 	bottom: 1px;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-sw {
 	cursor: sw-resize;
 	width: 9px;
@@ -160,7 +160,7 @@
 	left: -5px;
 	bottom: -5px;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-nw {
 	cursor: nw-resize;
 	width: 9px;
@@ -168,7 +168,7 @@
 	left: -5px;
 	top: -5px;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-ne {
 	cursor: ne-resize;
 	width: 9px;