samples/basic: Switch from native_posix to native_sim

In the docs replace the references to native_posix with native_sim.
And switch the default test platform to native_sim from native_posix.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

samples/basic/hash_map/README.rst

@@ -16,16 +16,16 @@ This is a simple example that repeatedly:
 Building
 ********
 
-This application can be built on native_posix as follows:
+This application can be built on :ref:`native_sim <native_sim>` as follows:
 
 .. zephyr-app-commands::
    :zephyr-app: samples/basic/hash_map
    :host-os: unix
-   :board: native_posix
+   :board: native_sim
    :goals: build
    :compact:
 
-To build for another board, change "native_posix" above to that board's name.
+To build for another board, change "native_sim" above to that board's name.
 
 Additionally, it is possible to use one of the other Hashmap implementations by specifying
 

samples/basic/sys_heap/README.rst

@@ -10,18 +10,18 @@ A simple sample that can be used with any :ref:`supported board <boards>` and
 prints system heap usage to the console.
 
 Building
-********************
+********
 
-This application can be built on native_posix as follows:
+This application can be built on :ref:`native_sim <native_sim>` as follows:
 
 .. zephyr-app-commands::
    :zephyr-app: samples/basic/sys_heap
    :host-os: unix
-   :board: native_posix
+   :board: native_sim
    :goals: build
    :compact:
 
-To build for another board, change "native_posix" above to that board's name.
+To build for another board, change "native_sim" above to that board's name.
 
 Running
 *******

samples/basic/sys_heap/sample.yaml

@@ -3,7 +3,7 @@ sample:
   name: Basic system heap sample
 common:
   integration_platforms:
-    - native_posix
+    - native_sim
   harness: console
   harness_config:
     type: multi_line