Add support to get max length integer value via integer id

[luongvo]

What happened 🤔

• attrs.getAttributeIntValue(XML_NAMESPACE_ANDROID, "maxLength", 4) doesn't support to get max length int value from an integer id.

Insight 👀

• The default way to support getting int value from int id value is using TypeArray.getInt(com.android.internal.R.styleable.TextView_maxLength, -1), but custom PinEntryEditText class can't access to com.android.internal.R.styleable.TextView_maxLength.

• There is another approach to get the current value of max length from android:maxLength property. android:maxLength was initialized via TextView into InputFilter.LengthFilter, so we could get this value out from current filter list. Note that, InputFilter.LengthFilter.getMax() is only supported from API 21, so we need to use reflection to get mMax value out in lower APIs. mMax field was introduced from the first version of InputFilter https://android.googlesource.com/platform/frameworks/base/+/54b6cfa9a9e5b861a9930af873580d6dc20f773c/core/java/android/text/InputFilter.java

• After rechecked, it seems getting value out from mMax by reflection on API 19 is not a pretty way, back to getting value from resid or raw int value https://stackoverflow.com/a/60593495.

PoW (a.k.a Proof Of Work)💪

• API 21

• API 19

[MarcinB85]

Can we merge this PR?

[luongvo]

@MarcinB85 while waiting for the author merge this PR, you can use this version https://jitpack.io/#nimblehq/PinEntryEditText/feature~support-integer-id-value-on-max-length-SNAPSHOT