Check same dex file for finding class descriptor string id

Use ClassDef for finding same dex file class descriptor string id
for vdex. Removes some calls to FindStringId, the remaining calls to
FindStringId are due to multidex or referring to types in the boot
class path.

Also check method index slot to see if we get lucky.

Host perf:
DexFile::FindStringId: 2.57% -> 0.94%

Not done for fields since these do not seem to reach the FindStringId
case accordingto perf. The remaining calls to FindStringId come from:
100.00% verifier::VerifierDeps::GetClassDescriptorStringId
-> 66.62% verifier::VerifierDeps::AddAssignability
-> 33.38% verifier::VerifierDeps::AddMethodResolution

FB install time: 35.54s -> 34.41s (avg of 40 samples at 960MHZ N6P).

Bug: 32641252

Test: test-art-host

Change-Id: If50408cf1be5c2d2127140780b8d5af66306939c