feat: add tab-completion in REPL and Meta.getModuleVariables API

Add tab-completion support to the interactive REPL by introducing a new `Meta.getModuleVariables` foreign method that returns all top-level variable names from a given module. The REPL's `run()` method now handles the tab key to append completions, and the `refreshLine` method accepts a boolean parameter to control whether completion hints are shown. Also fix the Ctrl-D exit logic (inverted condition) and remove the unused `EscapeBracket` class.

test/meta/get_module_variables.wren

@@ -0,0 +1,17 @@
+import "meta" for Meta
+
+var variables = Meta.getModuleVariables("main")
+
+// Includes implicitly imported core stuff.
+System.print(variables.contains("Object")) // expect: true
+System.print(variables.contains("Bool")) // expect: true
+
+// Includes top level variables.
+System.print(variables.contains("variables")) // expect: true
+
+// Even ones declared later.
+System.print(variables.contains("later")) // expect: true
+
+var later = "values"
+
+System.print(variables.contains("unknown")) // expect: false

test/meta/get_module_variables_not_string.wren

@@ -0,0 +1,3 @@
+import "meta" for Meta
+
+Meta.getModuleVariables(123) // expect runtime error: Module name must be a string.

test/meta/get_module_variables_unknown_module.wren

@@ -0,0 +1,3 @@
+import "meta" for Meta
+
+Meta.getModuleVariables("unknown") // expect runtime error: Could not find a module named 'unknown'.