grammar,compiler: Add Support For Fixed-Width Integers

Distinguishing between signed and unsigned fixed-width integer
types must still be done.

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

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

@@ -46,7 +46,7 @@ parser simple() {
 )
 
 =========================
-Simple Declaration (int)
+Simple Declaration (infinite-precision int)
 =========================
 parser simple() {
   state start {
@@ -73,7 +73,9 @@ parser simple() {
        (variableDeclaration
         (typeRef
          (baseType
-          (int)
+          (int_type
+           (int)
+          )
          )
         )
         (identifier)
@@ -92,6 +94,59 @@ parser simple() {
  )
 )
 
+=========================
+Simple Declaration (fixed-precision int)
+=========================
+parser simple() {
+  state start {
+    int<55> l;
+    transition accept;
+  }
+};
+
+---
+(p4program
+ (declaration
+  (parserDeclaration
+   (parserType
+    (parser)
+    (identifier)
+    (parameters)
+   )
+   (parserStates
+    (parserState
+     (state)
+     (identifier)
+     (parserStatements
+      (parserStatement
+       (variableDeclaration
+        (typeRef
+         (baseType
+          (int_type
+           (int)
+           (bit_width
+            (integer)
+           )
+          )
+         )
+        )
+        (identifier)
+       )
+      )
+     )
+     (parserTransitionStatement
+      (transition)
+      (transitionSelectionExpression
+       (identifier)
+      )
+     )
+    )
+   )
+  )
+ )
+)
+
+
 =========================
 Simple Declaration (string)
 =========================
@@ -331,7 +386,9 @@ bool functionb(bool a, int b) {
      (parameter
       (typeRef
        (baseType
-        (int)
+        (int_type
+         (int)
+        )
        )
       )
       (identifier)
@@ -393,7 +450,9 @@ bool functionb(in bool a, out int b, inout string c) {
        )
        (typeRef
         (baseType
-         (int)
+         (int_type
+          (int)
+         )
         )
        )
        (identifier)
@@ -468,7 +527,9 @@ extern bool functionb(in bool a, out int b, inout string c);
          )
          (typeRef
           (baseType
-           (int)
+           (int_type
+            (int)
+           )
           )
          )
          (identifier)