[PDF Ink Signatures] Parameterize PdfViewWebPluginInk.*Tests

Parameterize PdfViewWebPluginInk.*Tests so that they run with all
variations of the current feature parameters (e.g. text highlighting and
text annotations).

To do so, this CL performs the following:
1. Refactors PdfInkModuleTestVariation to make it reusable for
   PdfViewWebPluginInk.*Tests, by renaming and moving to a shared test
   helper file.
2. Removes the testing::TestWithParam subclassing from
   PdfViewWebPluginWithoutInitializeTest. The existing param is only
   needed in subclass PdfViewWebPluginWithDocInfoTest, so move it there.
   This allows PdfViewWebPluginInk.*Tests to still subclass
   PdfViewWebPluginWithoutInitializeTest and have a different param.

Bug: 342445982, 412730352
Change-Id: I31856f29c5576558ce04a37d15c83ea7a7504d93
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6477151
Commit-Queue: Andy Phan <andyphan@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1450699}