Represent byte, char and tree counts as 32 bit numbers

The parser spends the majority of its time allocating and freeing trees and stack nodes.
Also, the memory footprint of the AST is a significant concern when using tree-sitter
with large files. This library is already unlikely to work very well with source files
larger than 4GB, so representing rows, columns, byte lengths and child indices as
unsigned 32 bit integers seems like the right choice.

src/runtime/lexer.h

@@ -17,10 +17,10 @@ typedef struct {
   Length token_start_position;
 
   const char *chunk;
-  size_t chunk_start;
-  size_t chunk_size;
+  uint32_t chunk_start;
+  uint32_t chunk_size;
 
-  size_t lookahead_size;
+  uint32_t lookahead_size;
 
   TSInput input;
   TSLogger logger;