perf(es/parser): Remove start in State (#11201)

**Description:**

The only use of `start` is in the error span `read_digits`, so I think it can be removed.

Author: CPunisher

.changeset/sweet-pumas-prove.md

@@ -0,0 +1,6 @@
+---
+swc_core: patch
+swc_ecma_parser: patch
+---
+
+perf(es/parser): Remove `start` in `State`

crates/swc_ecma_parser/src/lexer/mod.rs

@@ -1212,7 +1212,7 @@ impl<'a> Lexer<'a> {
     }
 
     fn read_int_u32<const RADIX: u8>(&mut self, len: u8) -> LexResult<Option<u32>> {
-        let start = self.state().start();
+        let start = self.cur_pos();
 
         let mut count = 0;
         let v = self.read_digits::<_, Option<u32>, RADIX>(

crates/swc_ecma_parser/src/lexer/state.rs

@@ -34,7 +34,6 @@ pub struct State {
     /// TODO: Remove this field.
     is_first: bool,
     pub next_regexp: Option<BytePos>,
-    pub start: BytePos,
     pub prev_hi: BytePos,
 
     pub(super) token_value: Option<TokenValue>,
@@ -392,14 +391,6 @@ impl Lexer<'_> {
             return Ok(Token::Eof);
         }
 
-        // println!(
-        //     "\tContext: ({:?}) {:?}",
-        //     self.input.cur().unwrap(),
-        //     self.state.context.0
-        // );
-
-        self.state.start = *start;
-
         self.read_token()
     }
 
@@ -499,8 +490,6 @@ impl Lexer<'_> {
             value: value.into(),
         });
 
-        self.state.start = start;
-
         Ok(Token::JSXText)
     }
 
@@ -587,7 +576,6 @@ impl State {
             had_line_break: false,
             is_first: true,
             next_regexp: None,
-            start: BytePos(0),
             prev_hi: start_pos,
             token_value: None,
             token_type: None,
@@ -625,11 +613,6 @@ impl State {
         self.prev_hi
     }
 
-    #[inline(always)]
-    pub fn start(&self) -> BytePos {
-        self.start
-    }
-
     pub fn can_have_trailing_line_comment(&self) -> bool {
         let Some(t) = self.token_type() else {
             return true;