[ruby/prism] Allow command calls in endless method bodies regardless of context

Previously, endless method definitions like `x = def f = p 1` would fail
to parse because command calls (method calls without parentheses) were
only accepted when the surrounding binding power was less than
`PM_BINDING_POWER_COMPOSITION` (8). In assignment contexts with binding
power 18, this condition was false, causing parse errors.

This fix ensures command calls are always accepted in endless method
bodies by passing `true` for `accepts_command_call`, making the method
body parse consistently regardless of where the method is defined.

ruby/prism@70413ed4dd

Author: st0012

prism/prism.c

@@ -19520,7 +19520,7 @@ parse_expression_prefix(pm_parser_t *parser, pm_binding_power_t binding_power, b
                 pm_do_loop_stack_push(parser, false);
                 statements = (pm_node_t *) pm_statements_node_create(parser);
 
-                pm_node_t *statement = parse_expression(parser, PM_BINDING_POWER_DEFINED + 1, binding_power < PM_BINDING_POWER_COMPOSITION, false, PM_ERR_DEF_ENDLESS, (uint16_t) (depth + 1));
+                pm_node_t *statement = parse_expression(parser, PM_BINDING_POWER_DEFINED + 1, true, false, PM_ERR_DEF_ENDLESS, (uint16_t) (depth + 1));
 
                 if (accept1(parser, PM_TOKEN_KEYWORD_RESCUE_MODIFIER)) {
                     context_push(parser, PM_CONTEXT_RESCUE_MODIFIER);

test/prism/fixtures/endless_methods.txt

@@ -3,3 +3,5 @@ def foo = 1
 def bar = A ""
 
 def method = 1 + 2 + 3
+
+x = def f = p 1