8350938: ResourceParsingClassHierarchyResolver inflates all Utf8 CP entries

[trevorkbond]

Enhance ResourceParsingClassHierarchyResolver.getClassInfo to use ClassReaderImpl to improve performance. Previously this method inflated and stored all UTF-8 entries in the constant pool and later accessed the array of strings to try finding the name of the superclass. ClassReaderImpl instead stores constant pool offsets and later lazily reads/inflates UTF8 entries as needed.

I’ve ran all tier 1 tests and tests within test/jdk/jdk/classfile on the latest version of this change, and they all pass.

I ran some informal performance testing to see if these changes led to any improvement. I created a .class file with several thousand unique strings in a String array to deliberately enlarge the number of UTF-8 entries in the constant pool. I then benchmarked the performance of running a process nearly identical to ClassHierarchyInfoTest.testClassLoaderParsingResolver on this custom class over 200 runs using JMH. The results are as follows.

Version	Avg Time (ns/op)	Δ vs Before
Before	1,483,671.539 ± 3,477.744	—
After	1,380,064.517 ± 3,482.434	≈ 7.0% faster

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Issue

• JDK-8350938: ResourceParsingClassHierarchyResolver inflates all Utf8 CP entries (Enhancement - P5)

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[dansmithcode]

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