feat: convert fiber tests to use block arguments instead of anonymous function literals

Update all fiber test files to replace `Fiber.create(fn { ... })` with `Fiber.create { ... }` block syntax, and add compiler support for parsing block bodies without requiring a newline after the opening brace. The compiler changes include removing `TOKEN_LEFT_BRACE` from the newline-discarding token list and adding `match(compiler, TOKEN_LINE)` calls in `finishBlock`, `methodCall`, `function`, and `block` to handle empty block bodies and inline expressions.

test/fiber/resume_caller.wren

@@ -1,12 +1,12 @@
-var b = Fiber.create(fn {
+var b = Fiber.create {
   IO.print("fiber b")
-})
+}
 
-var a = Fiber.create(fn {
+var a = Fiber.create {
   IO.print("begin fiber a")
   b.run
   IO.print("end fiber a")
-})
+}
 
 IO.print("begin main")
 a.run