Disallow refinements in GivenTypes

Test case is i2567.scala. We would like to write
```
class Foo given T {
  ...
}
```
But previously this mistook the class body as a refinement for `T`.

Author: odersky

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2088,7 +2088,7 @@ object Parsers {
      *  ClsParam          ::=  {Annotation} [{ParamModifier} (`val' | `var') | `inline'] Param
      *  DefParamClause    ::=  [nl] `(' [FunArgMods] [DefParams] ')' | InferParamClause
      *  InferParamClause  ::=  ‘given’ (‘(’ DefParams ‘)’ | ContextTypes)
-     *  ContextTypes      ::=  RefinedType {`,' RefinedType}
+     *  ContextTypes      ::=  AnnotType {`,' AnnotType}
      *  DefParams         ::=  DefParam {`,' DefParam}
      *  DefParam          ::=  {Annotation} [`inline'] Param
      *  Param             ::=  id `:' ParamType [`=' Expr]
@@ -2209,7 +2209,7 @@ object Parsers {
           params :: (if (lastClause) Nil else recur(firstClause = false, nparams + params.length))
         }
         else if (isContextual) {
-          val tps = commaSeparated(refinedType)
+          val tps = commaSeparated(() => annotType())
           var counter = nparams
           def nextIdx = { counter += 1; counter }
           val params = tps.map(makeSyntheticParameter(nextIdx, _, Given | Implicit))
@@ -2618,8 +2618,8 @@ object Parsers {
 
     /** InstanceDef    ::=  [id] InstanceParams InstanceBody
      *  InstanceParams ::=  [DefTypeParamClause] {InferParamClause}
-     *  InstanceBody   ::=  [‘of’ ConstrApp {‘,’ ConstrApp }] [TemplateBody]
-     *                   |  ‘of’ Type ‘=’ Expr
+     *  InstanceBody   ::=  [‘for’ ConstrApp {‘,’ ConstrApp }] [TemplateBody]
+     *                   |  ‘for’ Type ‘=’ Expr
      */
     def instanceDef(start: Offset, mods: Modifiers, instanceMod: Mod) = atSpan(start, nameStart) {
       var mods1 = addMod(mods, instanceMod)

docs/docs/internals/syntax.md

@@ -304,7 +304,7 @@ DefParamClause    ::=  [nl] ‘(’ [DefParams] ‘)’ | InferParamClause
 InferParamClause  ::=  ‘given’ (‘(’ [DefParams] ‘)’ | ContextTypes)
 DefParams         ::=  DefParam {‘,’ DefParam}
 DefParam          ::=  {Annotation} [‘inline’] Param                            ValDef(mods, id, tpe, expr) -- point of mods at id.
-ContextTypes      ::=  RefinedType {‘,’ RefinedType}
+ContextTypes      ::=  AnnotType {‘,’ AnnotType}
 FunArgMods        ::=  { ‘implicit’ | ‘erased’ }
 ClosureMods       ::=  { ‘implicit’ | ‘erased’ | ‘given’}
 ```
@@ -357,7 +357,6 @@ Def               ::=  ‘val’ PatDef
                     |  ‘var’ VarDef
                     |  ‘def’ DefDef
                     |  ‘type’ {nl} TypeDcl
-                    |  ‘instance’ {nl} InstanceDef
                     |  TmplDef
                     |  INT
 PatDef            ::=  Pattern2 {‘,’ Pattern2} [‘:’ Type] ‘=’ Expr              PatDef(_, pats, tpe?, expr)
@@ -380,8 +379,8 @@ ObjectDef         ::=  id [Template]
 EnumDef           ::=  id ClassConstr InheritClauses EnumBody                   EnumDef(mods, name, tparams, template)
 InstanceDef       ::=  [id] InstanceParams InstanceBody
 InstanceParams    ::=  [DefTypeParamClause] {InferParamClause}
-InstanceBody      ::=  [‘of’ ConstrApp {‘,’ ConstrApp }] [TemplateBody]
-                    |  ‘of’ Type ‘=’ Expr
+InstanceBody      ::=  [‘for’ ConstrApp {‘,’ ConstrApp }] [TemplateBody]
+                    |  ‘for’ Type ‘=’ Expr
 Template          ::=  InheritClauses [TemplateBody]                            Template(constr, parents, self, stats)
 InheritClauses    ::=  [‘extends’ ConstrApps] [‘derives’ QualId {‘,’ QualId}]
 ConstrApps        ::=  ConstrApp {‘with’ ConstrApp}

tests/run/i2567.check

@@ -0,0 +1,6 @@
+hi
+hi
+hi
+hi
+hi
+hi

tests/run/i2567.scala

@@ -0,0 +1,15 @@
+class TC
+implied tc for TC
+
+class Foo given TC {
+  println("hi")
+}
+
+object Test extends App {
+  new Foo
+  new Foo given tc
+  new Foo()
+  new Foo() given tc
+  Foo()
+  Foo() given tc
+}