hclsyntax: Copy only tok.Range instead of whole object

Doing this reduces the memory used in ~11%, as the following benchstat
comparison shows:

    name          old time/op    new time/op    delta
    LexConfig-12    9.27µs ± 0%    9.03µs ± 1%   -2.55%  (p=0.000 n=9+10)

    name          old alloc/op   new alloc/op   delta
    LexConfig-12    8.94kB ± 0%    7.98kB ± 0%  -10.74%  (p=0.000 n=10+10)

    name          old allocs/op  new allocs/op  delta
    LexConfig-12      37.0 ± 0%      37.0 ± 0%     ~     (all equal)

Benchmarks were created using:

    go test -benchmem -benchtime=200000x -count=10 -bench=.

1 files changed, 11 insertions, 12 deletions

diff --git a/hclsyntax/token.go b/hclsyntax/token.go
index f4c6c93..4fe26a1 100644
--- a/hclsyntax/token.go
+++ b/hclsyntax/token.go
@@ -191,8 +191,7 @@ func checkInvalidTokens(tokens Tokens) hcl.Diagnostics {
 	toldBadUTF8 := 0
 
 	for _, tok := range tokens {
-		// copy token so it's safe to point to it
-		tok := tok
+		tokRange := tok.Range
 
 		switch tok.Type {
 		case TokenBitwiseAnd, TokenBitwiseOr, TokenBitwiseXor, TokenBitwiseNot:
@@ -211,7 +210,7 @@ func checkInvalidTokens(tokens Tokens) hcl.Diagnostics {
 					Severity: hcl.DiagError,
 					Summary:  "Unsupported operator",
 					Detail:   fmt.Sprintf("Bitwise operators are not supported.%s", suggestion),
-					Subject:  &tok.Range,
+					Subject:  &tokRange,
 				})
 				toldBitwise++
 			}
@@ -221,7 +220,7 @@ func checkInvalidTokens(tokens Tokens) hcl.Diagnostics {
 					Severity: hcl.DiagError,
 					Summary:  "Unsupported operator",
 					Detail:   "\"**\" is not a supported operator. Exponentiation is not supported as an operator.",
-					Subject:  &tok.Range,
+					Subject:  &tokRange,
 				})
 
 				toldExponent++
@@ -234,7 +233,7 @@ func checkInvalidTokens(tokens Tokens) hcl.Diagnostics {
 					Severity: hcl.DiagError,
 					Summary:  "Invalid character",
 					Detail:   "The \"`\" character is not valid. To create a multi-line string, use the \"heredoc\" syntax, like \"<<EOT\".",
-					Subject:  &tok.Range,
+					Subject:  &tokRange,
 				})
 			}
 			if toldBacktick <= 2 {
@@ -246,7 +245,7 @@ func checkInvalidTokens(tokens Tokens) hcl.Diagnostics {
 					Severity: hcl.DiagError,
 					Summary:  "Invalid character",
 					Detail:   "Single quotes are not valid. Use double quotes (\") to enclose strings.",
-					Subject:  &tok.Range,
+					Subject:  &tokRange,
 				}
 				diags = append(diags, newDiag)
 			}
@@ -259,7 +258,7 @@ func checkInvalidTokens(tokens Tokens) hcl.Diagnostics {
 					Severity: hcl.DiagError,
 					Summary:  "Invalid character",
 					Detail:   "The \";\" character is not valid. Use newlines to separate arguments and blocks, and commas to separate items in collection values.",
-					Subject:  &tok.Range,
+					Subject:  &tokRange,
 				})
 
 				toldSemicolon++
@@ -270,7 +269,7 @@ func checkInvalidTokens(tokens Tokens) hcl.Diagnostics {
 					Severity: hcl.DiagError,
 					Summary:  "Invalid character",
 					Detail:   "Tab characters may not be used. The recommended indentation style is two spaces per indent.",
-					Subject:  &tok.Range,
+					Subject:  &tokRange,
 				})
 
 				toldTabs++
@@ -281,7 +280,7 @@ func checkInvalidTokens(tokens Tokens) hcl.Diagnostics {
 					Severity: hcl.DiagError,
 					Summary:  "Invalid character encoding",
 					Detail:   "All input files must be UTF-8 encoded. Ensure that UTF-8 encoding is selected in your editor.",
-					Subject:  &tok.Range,
+					Subject:  &tokRange,
 				})
 
 				toldBadUTF8++
@@ -291,7 +290,7 @@ func checkInvalidTokens(tokens Tokens) hcl.Diagnostics {
 				Severity: hcl.DiagError,
 				Summary:  "Invalid multi-line string",
 				Detail:   "Quoted strings may not be split over multiple lines. To produce a multi-line string, either use the \\n escape to represent a newline character or use the \"heredoc\" multi-line template syntax.",
-				Subject:  &tok.Range,
+				Subject:  &tokRange,
 			})
 		case TokenInvalid:
 			chars := string(tok.Bytes)
@@ -301,14 +300,14 @@ func checkInvalidTokens(tokens Tokens) hcl.Diagnostics {
 					Severity: hcl.DiagError,
 					Summary:  "Invalid character",
 					Detail:   "\"Curly quotes\" are not valid here. These can sometimes be inadvertently introduced when sharing code via documents or discussion forums. It might help to replace the character with a \"straight quote\".",
-					Subject:  &tok.Range,
+					Subject:  &tokRange,
 				})
 			default:
 				diags = append(diags, &hcl.Diagnostic{
 					Severity: hcl.DiagError,
 					Summary:  "Invalid character",
 					Detail:   "This character is not used within the language.",
-					Subject:  &tok.Range,
+					Subject:  &tokRange,
 				})
 			}
 		}