Add title.content alias for Title::getContent()

No other access in the Title class contains a `get` prefix, so this
makes the title methods consistent.

Bug: T373047
Change-Id: I4a3a7498462b7b3b6143dc61f529e526ccb112e2

includes/Engines/LuaCommon/lualib/mw.title.lua

@@ -168,6 +168,7 @@ local function makeTitleObject( data )
 	end
 
 	function data:getContent()
+		-- deprecated: should use `title.content` instead
 		checkSelf( self, 'getContent' )
 		local content = php.getContent( self.fullText )
 		data.getContent = function ( self )
@@ -301,6 +302,12 @@ local function makeTitleObject( data )
 				end
 				return data.redirectTarget
 			end
+			if k == 'content' then
+				if data.content == nil then
+					data.content = php.getContent( data.prefixedText ) or false
+				end
+				return data.content
+			end
 			if k == 'categories' then
 				if data.categories == nil then
 					data.categories = php.getCategories( data.prefixedText )

tests/phpunit/Engines/LuaCommon/TitleLibraryTests.lua

@@ -75,6 +75,11 @@ local function test_getContent()
 		mw.title.new( 'ScribuntoTestNonExistingPage' ):getContent()
 end
 
+local function test_content()
+	return mw.title.new( 'ScribuntoTestPage' ).content,
+		mw.title.new( 'ScribuntoTestNonExistingPage' ).content
+end
+
 local function test_redirectTarget()
 	local targets = {}
 	local titles = {
@@ -412,6 +417,13 @@ local tests = {
 		}
 	},
 
+	{ name = '.content', func = test_content,
+		expect = {
+			'{{int:mainpage}}<includeonly>...</includeonly><noinclude>...</noinclude>',
+			false,
+		}
+	},
+
 	{ name = '.redirectTarget', func = test_redirectTarget, type = 'ToString',
 		expect = { 'ScribuntoTestTarget', false, false }
 	},