Add Instantations to Grammar

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

tree-sitter-p4/test/corpus/statements.txt

@@ -45,8 +45,8 @@ parser simple() {
     )
    )
   )
-  (semicolon)
  )
+ (semicolon)
 )
 
 =========================
@@ -101,8 +101,8 @@ parser simple() {
     )
    )
   )
-  (semicolon)
  )
+ (semicolon)
 )
 
 =========================
@@ -181,7 +181,7 @@ parser simple() {
     )
    )
   )
-  (semicolon)
  )
+ (semicolon)
 )