Change syntax of ConstrApps

The previous syntax was unparseable without major contortions in the Parser.

Author: odersky

docs/docs/internals/syntax.md

@@ -386,8 +386,9 @@ Template          ::=  InheritClauses [TemplateBody]
 InheritClauses    ::=  [‘extends’ ConstrApps] [‘derives’ QualId {‘,’ QualId}]
 ConstrApps        ::=  ConstrApp {‘with’ ConstrApp}
                     |  ConstrApp {‘,’ ConstrApp}
-ConstrApp         ::=  AnnotType {ArgumentExprs}                                Apply(tp, args)
-                    |  ‘(’ ConstrApp {‘given’ (InfixExpr | ParArgumentExprs)} ‘)’
+ConstrApp         ::=  SimpleConstrApp
+                    |  ‘(’ SimpleConstrApp {‘given’ (PrefixExpr | ParArgumentExprs)} ‘)’
+SimpleConstrApp   ::=  AnnotType {ArgumentExprs}                                Apply(tp, args)
 ConstrExpr        ::=  SelfInvocation
                     |  ConstrBlock
 SelfInvocation    ::=  ‘this’ ArgumentExprs {ArgumentExprs}

docs/docs/reference/contextual-implicit/instance-defs.md

@@ -75,8 +75,9 @@ TmplDef          ::=  ...
 InstanceDef      ::=  [id] [DefTypeParamClause] InstanceBody
 InstanceBody     ::=  [‘for’ ConstrApp {‘,’ ConstrApp }] {GivenParamClause} [TemplateBody]
                    |  ‘for’ Type {GivenParamClause} ‘=’ Expr
-ConstrApp        ::=  AnnotType {ArgumentExprs}
-                   |  ‘(’ ConstrApp {‘given’ (InfixExpr | ParArgumentExprs)} ‘)’
+ConstrApp        ::=  SimpleConstrApp
+                   |  ‘(’ SimpleConstrApp {‘given’ (PrefixExpr | ParArgumentExprs)} ‘)’
+SimpleConstrApp  ::=  AnnotType {ArgumentExprs}
 GivenParamClause ::=  ‘given’ (‘(’ [DefParams] ‘)’ | GivenTypes)
 GivenTypes       ::=  AnnotType {‘,’ AnnotType}
 ```

docs/docs/reference/contextual/instance-defs.md

@@ -72,6 +72,8 @@ GivenParamClause ::=  ‘given’ (‘(’ [DefParams] ‘)’ | GivenTypes)
 InstanceBody     ::=  [‘for’ ConstrApp {‘,’ ConstrApp }] [TemplateBody]
                    |  ‘for’ Type ‘=’ Expr
 GivenTypes       ::=  AnnotType {‘,’ AnnotType}
+ConstrApp        ::=  SimpleConstrApp
+                   |  ‘(’ SimpleConstrApp {‘given’ (PrefixExpr | ParArgumentExprs)} ‘)’
 ```
 The identifier `id` can be omitted only if either the `for` part or the template body is present.
 If the `for` part is missing, the template body must define at least one extension method.