Uncomment syncs before adaptivePredict

These allow slightly better error recovery before we run
`adaptivePredict`, as illustrated by the test.

runtime-testsuite/resources/org/antlr/v4/test/runtime/templates/ParserErrors/Index.stg

@@ -11,6 +11,7 @@ TestTemplates ::= [
 	"LL2": [],
 	"LL3": [],
 	"LLStar": [],
+	"SingleTokenDeletionBeforePredict": [],
 	"SingleTokenDeletionBeforeLoop": [],
 	"MultiTokenDeletionBeforeLoop": [],
 	"SingleTokenDeletionDuringLoop": [],

runtime-testsuite/resources/org/antlr/v4/test/runtime/templates/ParserErrors/SingleTokenDeletionBeforePredict.stg

@@ -0,0 +1,28 @@
+TestType() ::= "Parser"
+
+Options ::= [
+	"Debug": false
+]
+
+Grammar ::= [
+	"T": {<grammar("T")>}
+]
+
+Input() ::= "caaab"
+
+Rule() ::= "a"
+
+Output() ::= <<
+>>
+
+Errors() ::= <<
+line 1:0 extraneous input 'c' expecting 'a'
+>>
+
+grammar(grammarName) ::= <<
+grammar <grammarName>;
+a : 'a'+ 'b'
+  | 'a'+ 'c'
+;
+q : 'e' ;
+>>

tool/resources/org/antlr/v4/tool/templates/codegen/Java/Java.stg

@@ -531,7 +531,7 @@ do {
 
 AltBlock(choice, preamble, alts, error) ::= <<
 setState(<choice.stateNumber>);
-<!_errHandler.sync(this);!>
+_errHandler.sync(this);
 <if(choice.label)><labelref(choice.label)> = _input.LT(1);<endif>
 <preamble; separator="\n">
 switch ( getInterpreter().adaptivePredict(_input,<choice.decision>,_ctx) ) {
@@ -544,7 +544,7 @@ case <i>:
 
 OptionalBlock(choice, alts, error) ::= <<
 setState(<choice.stateNumber>);
-<!_errHandler.sync(this);!>
+_errHandler.sync(this);
 switch ( getInterpreter().adaptivePredict(_input,<choice.decision>,_ctx) ) {
 <alts:{alt |
 case <i><if(!choice.ast.greedy)>+1<endif>: