implement EspClass::getFreeContStack method (#5133)

* implement EspClass::getFreeContStack method

* Remove unneeded extern

* Really remove unneeded extern

Author: devyte

cores/esp8266/Esp.cpp

@@ -25,6 +25,7 @@
 #include "interrupts.h"
 #include "MD5Builder.h"
 #include "umm_malloc/umm_malloc.h"
+#include "cont.h"
 
 extern "C" {
 #include "user_interface.h"
@@ -177,6 +178,11 @@ uint16_t EspClass::getMaxFreeBlockSize(void)
     return umm_max_block_size();
 }
 
+uint32_t EspClass::getFreeContStack()
+{
+    return cont_get_free_stack(g_pcont);
+}
+
 uint32_t EspClass::getChipId(void)
 {
     return system_get_chip_id();

cores/esp8266/Esp.h

@@ -110,6 +110,8 @@ class EspClass {
         uint8_t getHeapFragmentation(); // in %
         void getHeapStats(uint32_t* free = nullptr, uint16_t* max = nullptr, uint8_t* frag = nullptr);
 
+        uint32_t getFreeContStack();
+
         const char * getSdkVersion();
         String getCoreVersion();
         String getFullVersion();