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Instead of copying libraries on M-, this changes to using the crazy
linker, which loads the library without any knowledge of what libraries
have been loaded by the system linker. This requires manual JNI
registration. To make sure we only register WebLayer JNI when needed,
a minimal set of JNI methods is registered, and the full set is
registered later if we require WebView compatibility.

In N+, we switch to prepending "/." to library paths instead of using
symlinks, which allows us to avoid writing any files to the apps data
directory. This simplifies the interface quite a bit, allowing
initializeWebViewCompatibilityMode() to be sync instead of async. I will
follow up with the Android team to make sure we have a better solution
for future versions of Android.

The API has not been used in the client app yet, so it should be safe
to remove M- support for the copy library approach in the
implementation. The old version of initializeWebViewCompatibilityMode()
was kept so the WebLayer API version compat tests would still pass.

TBR=agrieve@chromium.org

Bug: 1051358
Change-Id: I2cd5ae0e025feaeb5c41cf9ddfafc91cd09fbad7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2090024
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749973}