Add highlighting of double underscore Magic Words as __TOC__

For testing:
__NOTOC__
___NOTOC___
____NOTOC____
_____NOTOC_____
______NO!TOC__NOTOC____
______NO{{TOC}}_____
______NO[[TOC]]_____
______NO'''TOC'''_____
__nOtOc__
FFFFF___NOtoc______
'''____________NOTOC______'''
__TOC___TOC__
__TOC____TOC__
___TOC_____TOC___
__TOC___TOC__
___NOTOC___
____NOTOC____
_____NOTOC_____
______NO!TOC__NOTOC____
______NO{{TOC}}_____
______NO[[TOC]]_____
______NO'''TOC'''_____
__nOtOc__
FFFFF___NOtoc______
{{__TOC__|__TOC__}}

Wrong, but not a big problem:
[[__TOC__|__TOC__]]

Bug: T170041
Change-Id: I0b2cfd02550c2685d241bdf3596507c5972878d5

resources/mode/mediawiki/mediawiki.css

@@ -8,7 +8,7 @@
 
 .cm-mw-skipformatting { background-color: #adf; }
 .cm-mw-list { color: #08f; font-weight: bold; }
-.cm-mw-signature, .cm-mw-hr { color: #08f; font-weight: bold; background-color: #eee; }
+.cm-mw-doubleUnderscore, .cm-mw-signature, .cm-mw-hr { color: #08f; font-weight: bold; background-color: #eee; }
 .cm-mw-indenting { color: #08f; font-weight: bold; }
 .cm-mw-mnemonic { color: #290; }
 .cm-mw-comment { color: #aaa; font-weight: normal; }

resources/mode/mediawiki/mediawiki.js

@@ -807,6 +807,29 @@
 							return 'mw-signature';
 						}
 						break;
+					case '_': // Maybe double undescored Magic Word as __TOC__
+						tmp = 1;
+						while ( stream.eat( '_' ) ) { // Optimize processing of many underscore symbols
+							tmp++;
+						}
+						if ( tmp > 2 ) { // Many underscore symbols
+							if ( !stream.eol() ) {
+								stream.backUp( 2 ); // Leave last two underscore symbols for processing again in next iteration
+							}
+							return makeStyle( style, state ); // Optimization: skip regex function at the end for EOL and backuped symbols
+						} else if ( tmp === 2 ) { // Check on double underscore Magic Word
+							name = stream.match( /([^\s\u00a0>}[\]<{'|&:~]+?)__/ ); // The same as the end of function except '_' inside and with '__' at the end of string
+							if ( name && name[ 0 ] ) {
+								if ( '__' + name[ 0 ].toLowerCase() in mwConfig.doubleUnderscore[ 0 ] || '__' + name[ 0 ] in mwConfig.doubleUnderscore[ 1 ] ) {
+									return 'mw-doubleUnderscore';
+								}
+								if ( !stream.eol() ) {
+									stream.backUp( 2 ); // Two underscore symbols at the end can be begining of other double undescored Magic Word
+								}
+								return makeStyle( style, state ); // Optimization: skip regex function at the end for EOL and backuped symbols
+							}
+						}
+						break;
 					default:
 						if ( /[\s\u00a0]/.test( ch ) ) {
 							stream.eatSpace();