Introduces Bytes class (#1019)

This introduces a new `Bytes` standard library class, for working with
binary data.

* Add Bytes class to the standard library
* Change CLI to eval `output.bytes`
* Change code generators to map Bytes to respective underlying type
* Add subscript and concat operator support
* Add binary encoding for Bytes
* Add PCF and Plist rendering for Bytes

Co-authored-by: Kushal Pisavadia <kushi.p@gmail.com>

pkl-server/src/test/kotlin/org/pkl/server/AbstractServerTest.kt

@@ -632,7 +632,7 @@ abstract class AbstractServerTest {
             content
             
             $tripleQuote
-          base64 = "Y29udGVudAo="
+          bytes = Bytes(99, 111, 110, 116, 101, 110, 116, 10)
         }
         res2 {
           uri = "modulepath:/dir1/resource1.txt"
@@ -640,7 +640,7 @@ abstract class AbstractServerTest {
             content
             
             $tripleQuote
-          base64 = "Y29udGVudAo="
+          bytes = Bytes(99, 111, 110, 116, 101, 110, 116, 10)
         }
         res3 {
           ressy = "the module2 output"