Replace ANTLR with hand-rolled parser (#917)

Co-authored-by: Kushal Pisavadia <kushi.p@gmail.com>
Co-authored-by: Daniel Chao <daniel.h.chao@gmail.com>

pkl-core/src/main/resources/org/pkl/core/errorMessages.properties

@@ -797,7 +797,8 @@ Modifier `const` cannot be applied to property `{0}`.\n\
 Property `{0}` cannot be declared const, because it overrides a non-const property on parent class `{1}`.
 
 unseparatedObjectMembers=\
-Object members must be separated by whitespace, newline, or semicolon.
+Object members must be separated by whitespace, newline, or semicolon.\n\
+Object entries must be separated by newline or semicolon.
 
 unsupportedResourceType=\
 Resource reader `{0}` returned unsupported resource type `{1}`.
@@ -1126,3 +1127,58 @@ External {0} reader does not support scheme `{1}`.
 
 externalReaderAlreadyTerminated=\
 External reader process has already terminated.
+
+keywordNotAllowedHere=\
+Keyword `{0}` is not allowed here.\n\
+\n\
+If you must use this name as identifier, enclose it in backticks.
+
+unexpectedEndOfFile=\
+Unexpected end of file.
+
+wrongHeaders=\
+{0} cannot have doc comments, annotations or modifiers.
+
+invalidTopLevelToken=\
+Invalid token at position. Expected a class, typealias, method, or property.
+
+interpolationInConstant=\
+String constant cannot have interpolated values.
+
+unexpectedToken=\
+Unexpected token `{0}`. Expected `{1}`.
+
+unexpectedToken2=\
+Unexpected token `{0}`. Expected `{1}` or `{2}`.
+
+unexpectedTokenForExpression=\
+Unexpected token `{0}`.
+
+unexpectedTokenForType=\
+Unexpected token `{0}`. Expected a type.
+
+unexpectedTokenForType2=\
+Unexpected token `{0}`. Expected a type or `{1}`.
+
+typeAnnotationInAmends=\
+Properties with type annotations cannot have object bodies.\n\
+\n\
+To define both a type annotation and an object body, try using assignment instead.\n\
+For example: `obj: Bird = new { ... }`.
+
+invalidProperty=\
+Invalid property definition. Expected a type annotation, `=` or `{`.
+
+unexpectedCharacter=\
+Unexpected character `{0}`. Did you mean `{1}`?
+
+unexpectedCharacter3=\
+Unexpected character `{0}`. Did you mean `{1}`, `{2}` or `{3}`?
+
+invalidCharacter=\
+Invalid identifier `{0}`.
+
+danglingDocComment=\
+Dangling documentation comment.\n\
+\n\
+Documentation comments must be attached to modules, classes, typealiases, methods, or properties.