Generate bracketless tag id in FreeMarker forms

Before this change if FreeMarker Spring form macro was bound to a path
which contains square brackets, those brackets would also appear in id
of generated tag, making the id invalid.

As of this fix all FreeMarker Spring form macros generate tag with id
that does not contain square brackets.

Issue: SPR-8732

spring-webmvc/src/test/java/org/springframework/web/servlet/view/freemarker/FreeMarkerMacroTests.java

@@ -260,6 +260,11 @@ public class FreeMarkerMacroTests {
 		assertTrue("Wrong output: " + output, output.contains("<input type=\"checkbox\" id=\"jedi\" name=\"jedi\" checked=\"checked\" />"));
 	}
 
+	@Test
+	public void testForm17() throws Exception {
+		assertEquals("<input type=\"text\" id=\"spouses0.name\" name=\"spouses[0].name\" value=\"Fred\"     >", getMacroOutput("FORM17"));
+	}
+
 	private String getMacroOutput(String name) throws Exception {
 
 		String macro = fetchMacro(name);

spring-webmvc/src/test/java/org/springframework/web/servlet/view/freemarker/test.ftl

@@ -86,3 +86,6 @@ FORM15
 
 FORM16
 <@spring.formCheckbox "command.jedi"/>
+
+FORM17
+<@spring.formInput "command.spouses[0].name", ""/>