Change SparkFun_APDS9960 to submodule (#2800)

Submodule allows easier maintenance and tracking of upstream changes.
Only one function change, addition of `getStatusRegister` function.

Also patch fixing issue flagged by clang build:

```
 /home/runner/work/Sming/Sming/Sming/Libraries/SparkFun_APDS9960/SparkFun_APDS9960.cpp:508:32:
warning: result of comparison of constant -1 with expression of type 'uint8_t' (aka 'unsigned char') is always false
[-Wtautological-constant-out-of-range-compare]
                if( bytes_read == -1 ) {
                    ~~~~~~~~~~ ^  ~~
```

.gitmodules

@@ -349,6 +349,10 @@
 	path = Sming/Libraries/SolarCalculator
 	url = https://github.com/mikee47/SolarCalculator
 	ignore = dirty
+[submodule "Libraries.SparkFun_APDS9960"]
+	path = Sming/Libraries/SparkFun_APDS9960
+	url = https://github.com/sparkfun/SparkFun_APDS-9960_Sensor_Arduino_Library
+	ignore = dirty
 [submodule "Libraries.spiffs"]
 	path = Sming/Libraries/Spiffs/spiffs
 	url = https://github.com/pellepl/spiffs.git

Sming/Libraries/.patches/SparkFun_APDS9960.patch

@@ -0,0 +1,29 @@
+diff --git a/src/SparkFun_APDS9960.cpp b/src/SparkFun_APDS9960.cpp
+index 530c1f6..25968d0 100644
+--- a/src/SparkFun_APDS9960.cpp
++++ b/src/SparkFun_APDS9960.cpp
+@@ -163,7 +163,7 @@ bool SparkFun_APDS9960::init()
+         return false;
+     }
+
+-#if 0
++#if DEBUG
+     /* Gesture config register dump */
+     uint8_t reg;
+     uint8_t val;
+@@ -518,12 +518,13 @@ int SparkFun_APDS9960::readGesture()
+
+             /* If there's stuff in the FIFO, read it into our data block */
+             if( fifo_level > 0) {
+-                bytes_read = wireReadDataBlock(  APDS9960_GFIFO_U, 
++                int res = wireReadDataBlock(  APDS9960_GFIFO_U, 
+                                                 (uint8_t*)fifo_data, 
+                                                 (fifo_level * 4) );
+-                if( bytes_read == -1 ) {
++                if( res == -1 ) {
+                     return ERROR;
+                 }
++                bytes_read = res;
+ #if DEBUG
+                 Serial.print("FIFO Dump: ");
+                 for ( i = 0; i < bytes_read; i++ ) {

Sming/Libraries/.patches/SparkFun_APDS9960/component.mk

@@ -0,0 +1,2 @@
+COMPONENT_INCDIRS := src
+COMPONENT_SRCDIRS := src