Fix API usage typos (#502)

Author: jack-berg

doc-snippets/api/src/main/java/otel/AsyncCounterUsage.java

@@ -26,7 +26,7 @@ public static void asyncCounterUsage(Meter meter) {
             // Uncomment to optionally change the type to double
             // .ofDoubles()
             .buildWithCallback(
-                // the callback is invoked a MetricReader reads metrics
+                // the callback is invoked when a MetricReader reads metrics
                 observableMeasurement -> {
                   long currentWidgetCount = widgetCount.get();
 

doc-snippets/api/src/main/java/otel/AsyncGaugeUsage.java

@@ -25,7 +25,7 @@ public static void asyncGaugeUsage(Meter meter) {
             // Uncomment to optionally change the type to long
             // .ofLongs()
             .buildWithCallback(
-                // the callback is invoked a MetricReader reads metrics
+                // the callback is invoked when a MetricReader reads metrics
                 observableMeasurement -> {
                   double currentWidgetCount = processingLineTemp.get();
 

doc-snippets/api/src/main/java/otel/AsyncUpDownCounterUsage.java

@@ -25,7 +25,7 @@ public static void asyncUpDownCounterUsage(Meter meter) {
             // Uncomment to optionally change the type to double
             // .ofDoubles()
             .buildWithCallback(
-                // the callback is invoked a MetricReader reads metrics
+                // the callback is invoked when a MetricReader reads metrics
                 observableMeasurement -> {
                   long currentWidgetCount = queueLength.get();
 

doc-snippets/api/src/main/java/otel/ContextUsage.java

@@ -49,10 +49,10 @@ public static void contextUsage() throws Exception {
     ExecutorService executorService = Executors.newSingleThreadExecutor();
     ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(1);
 
-    // Context instances can be explicitly passed around application code, but its more convenient
+    // Context instances can be explicitly passed around application code, but it's more convenient
     // to use implicit context, calling Context.makeCurrent() and accessing via Context.current().
     // Context provides a number of utilities for implicit context propagation. These utilities wrap
-    // utility classes like Scheduler, and ExecutorService, ScheduledExecutorService, Runnable,
+    // utility classes like Scheduler, ExecutorService, ScheduledExecutorService, Runnable,
     // Callable, Consumer, Supplier, Function, etc and modify their behavior to call
     // Context.makeCurrent() before running.
     context.wrap(ContextUsage::callable).call();

doc-snippets/api/src/main/java/otel/GaugeUsage.java

@@ -14,7 +14,7 @@ public class GaugeUsage {
   private static final Attributes WIDGET_RED_CIRCLE = Util.WIDGET_RED_CIRCLE;
 
   public static void gaugeUsage(Meter meter) {
-    // Construct a gauge to record measurements as they occur when cannot be spatially
+    // Construct a gauge to record measurements as they occur, which cannot be spatially
     // re-aggregated.
     DoubleGauge gauge =
         meter