Replace dead links to ANTLR parser grammar (#973)

Author: bioball

docs/modules/language-reference/pages/index.adoc

@@ -7,8 +7,7 @@ include::ROOT:partial$component-attributes.adoc[]
 :uri-double-precision: https://en.wikipedia.org/wiki/Double-precision_floating-point_format
 :uri-progressive-disclosure: https://en.wikipedia.org/wiki/Progressive_disclosure
 :uri-javadoc-Pattern: https://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html
-:uri-github-PklLexer: {uri-github-tree}/pkl-core/src/main/antlr/PklLexer.g4
-:uri-github-PklParser: {uri-github-tree}/pkl-core/src/main/antlr/PklParser.g4
+:uri-github-PklLexer: {uri-github-tree}/pkl-core/src/main/java/org/pkl/core/parser/Lexer.java
 :uri-pkl-core-ModuleSchema: {uri-pkl-core-main-sources}/ModuleSchema.java
 :uri-pkl-core-SecurityManager: {uri-pkl-core-main-sources}/SecurityManager.java
 :uri-pkl-core-ResourceReader: {uri-pkl-core-main-sources}/resource/ResourceReader.java
@@ -5451,7 +5450,7 @@ They cannot be used as a regular identifier, and currently do not have any meani
 
 To use these names in an identifier, <<quoted-identifiers, surround them with backticks>>.
 
-For a complete list of keywords, consult link:{uri-github-PklLexer}[PklLexer.g4].
+For a complete list of keywords, consult field `Lexer.KEYWORDS` in {uri-github-PklLexer}[Lexer.java].
 
 [[blank-identifiers]]
 === Blank Identifiers