Support isInstanceOf(...) as implying non-null in assertion libraries.

[lazaroclapp]

Generally speaking, all these libraries implement the assertion by calling Class.isInstance, which
will return false whenever the argument is null. Similar to the instanceof operator:
https://docs.oracle.com/javase/1.5.0/docs/api/java/lang/Class.html#isInstance(java.lang.Object)

Given this, we can avoid some redundant assertions by adding knowledge about these calls directly
in AssertionsHandler.

[coveralls]

Pull Request Test Coverage Report for Build #1050

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.04%) to 93.057%

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Files with Coverage Reduction	New Missed Lines	%
../nullaway/src/main/java/com/uber/nullaway/handlers/MethodNameUtil.java	1	98.77%

Totals
Change from base Build #1047:	0.04%
Covered Lines:	5294
Relevant Lines:	5689

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💛 - Coveralls