term.ui: fix conflicting C struct declarations when compiling programs, importing term.ui before term, on windows

vlib/term/ui/1_term_and_ui_compilation_test.v

@@ -0,0 +1,8 @@
+import term.ui
+import term
+
+fn test_term_and_term_ui_can_compile_together() {
+	a := &ui.Context(0)
+	println('${term.bold('hello')} world ${int(a)}')
+	assert true
+}

vlib/term/ui/2_term_and_ui_compilation_test.v

@@ -0,0 +1,8 @@
+import term
+import term.ui
+
+fn test_term_and_term_ui_can_compile_together() {
+	a := &ui.Context(0)
+	println('${term.bold('hello')} world ${int(a)}')
+	assert true
+}

vlib/term/ui/consoleapi_windows.c.v

@@ -15,6 +15,7 @@ struct C.INPUT_RECORD {
 }
 
 union C.uChar {
+mut:
 	UnicodeChar rune
 	AsciiChar   byte
 }
@@ -54,12 +55,14 @@ struct C.FOCUS_EVENT_RECORD {
 
 [typedef]
 struct C.COORD {
+mut:
 	X i16
 	Y i16
 }
 
 [typedef]
 struct C.SMALL_RECT {
+mut:
 	Left   u16
 	Top    u16
 	Right  u16
@@ -68,6 +71,7 @@ struct C.SMALL_RECT {
 
 [typedef]
 struct C.CONSOLE_SCREEN_BUFFER_INFO {
+mut:
 	dwSize              C.COORD
 	dwCursorPosition    C.COORD
 	wAttributes         u16