RFR: 8294062: Improve parsing performance of j.l.c.MethodTypeDesc

[Adam Sotona]

Parsing performance of `j.l.c.MethodTypeDescriptor::ofDescriptor` can be significantly improved and add performance boost to intensive users.

Two main reasons have been identified and fixed in this patch:

First glitch is late insertion of return type to the first position of `j.u.ArrayList`, causing all previously parsed parameter types to shift using `System::arraycopy`.

Proposed patch inserts a placeholder for the return type first and replaces it with return type later.

Second performance degradation is in `MethodTypeDescriptor::skipOverFieldSignature`, where each identified class descriptor is exactly located by `String::indexOf`, extracted by `String::substring`, and passed for for the purpose of verification to `ConstantUtils::verifyUnqualifiedClassName`.

Proposed patch inlines the unqualified class name verification into `ConstantUtils::skipOverFieldSignature` parsing loop and so eliminates calls of `String::indexOf` and `String::substring`. Package private method `ConstantUtils::verifyUnqualifiedClassName` has no other use within the package, so it is removed.

Please review proposed performance improving patch.

Thanks,
Adam

-------------

Commit messages:
 - 8294062: Improve parsing performance of j.l.c.MethodTypeDesc

Changes: https://git.openjdk.org/jdk/pull/10358/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10358&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294062
  Stats: 39 lines in 1 file changed: 8 ins; 22 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/10358.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10358/head:pull/10358

PR: https://git.openjdk.org/jdk/pull/10358