Adding serial.set(Rx|Tx)BufferSize (#1931)

* Fix for https://github.com/Microsoft/pxt-microbit/issues/1929

* bump pxt

* updated docs

* fix default values

* moving dialogs to react

* moving to react

* typo

* typo

docs/reference/serial/set-rx-buffer-size.md

@@ -0,0 +1,23 @@
+# set Rx Buffer Size
+
+Sets the length of the serial reception buffer in bytes.
+
+```sig
+serial.setRxBufferSize(10)
+```
+
+## Parameters
+
+* **size**: desired length of the reception buffer
+
+## Example
+
+Allocates 64 bytes for the reception buffer.
+
+```typescript
+serial.setRxBufferSize(64)
+```
+
+## See also
+
+[set tx buffer size](/reference/serial/set-tx-buffer-size)

docs/reference/serial/set-tx-buffer-size.md

@@ -0,0 +1,23 @@
+# set Tx Buffer Size
+
+Sets the length of the serial transmission buffer in bytes.
+
+```sig
+serial.setTxBufferSize(10)
+```
+
+## Parameters
+
+* **size**: desired length of the transmission buffer
+
+## Example
+
+Allocates 64 bytes for the transmission buffer.
+
+```typescript
+serial.setTxBufferSize(64)
+```
+
+## See also
+
+[set rx buffer size](/reference/serial/set-rx-buffer-size)