Fix the javadoc warnings

Summary:
Fix below javadoc warnings:
```
/Users/simsun/fbsource/fbandroid/libraries/soloader/java/com/facebook/soloader/SoSource.java:95: warning: no param for soName
  protected File getSoFileByName(String soName) throws IOException {
                 ^
/Users/simsun/fbsource/fbandroid/libraries/soloader/java/com/facebook/soloader/SoSource.java:95: warning: no return
  protected File getSoFileByName(String soName) throws IOException {
                 ^
/Users/simsun/fbsource/fbandroid/libraries/soloader/java/com/facebook/soloader/SoSource.java:95: warning: no throws for java.io.IOException
  protected File getSoFileByName(String soName) throws IOException {
                 ^
Generating /var/folders/48/qgw4nzlj2p56xl344pd8rfh40000gn/T/tmp7j2fsb_l/com/facebook/soloader/AsyncInitSoSource.html...
Generating /var/folders/48/qgw4nzlj2p56xl344pd8rfh40000gn/T/tmp7j2fsb_l/com/facebook/soloader/BackupSoSource.html...
/Users/simsun/fbsource/fbandroid/libraries/soloader/java/com/facebook/soloader/UnpackingSoSource.java:484: warning: no throws for java.io.IOException
  public void prepareForceRefresh() throws IOException {
              ^
Generating /var/folders/48/qgw4nzlj2p56xl344pd8rfh40000gn/T/
```

Differential Revision: D52492588

fbshipit-source-id: b38e09417c50fa1a98d2996c45599e89c803a22b

java/com/facebook/soloader/SoSource.java

@@ -90,6 +90,10 @@ public abstract int loadLibrary(
   /**
    * Returns the so file for the specified library. Returns null if the library does not exist or if
    * it's not backed by a file.
+   *
+   * @param soName Name of library to load
+   * @return File if library found; {@code null} if not.
+   * @throws IOException IOException
    */
   @Nullable
   protected File getSoFileByName(String soName) throws IOException {

java/com/facebook/soloader/UnpackingSoSource.java

@@ -480,7 +480,11 @@ public String getLibraryPath(String soName) throws IOException {
     return soFile.getCanonicalPath();
   }
 
-  /** Prepare this SoSource by unconditonally unpacking/re-unpacking it. */
+  /**
+   * Prepare this SoSource by unconditonally unpacking/re-unpacking it.
+   *
+   * @throws IOException IOException
+   */
   public void prepareForceRefresh() throws IOException {
     prepare(SoSource.PREPARE_FLAG_FORCE_REFRESH);
   }

java/com/facebook/soloader/recovery/RecoveryStrategyFactory.java

@@ -18,7 +18,7 @@
 
 public interface RecoveryStrategyFactory {
   /**
-   * @returns an instance of RecoveryStrategy that will be used to recover from failures to load a
+   * @return an instance of RecoveryStrategy that will be used to recover from failures to load a
    *     native library. The recover method of the returned object might be called multiple times
    *     until false is returned or until a successfull retry of the load is performed. All calls
    *     are guaranteed to hapen sequentially, within the context of a single library load. This