Reland "jni_generator: Revamp CLI"

This reverts commit e4338c97c4e9d19c0aae6d0e5b9c07808b8b5c04.

Reason for reland: Will use "python3.8" when "python3" links to
a lesser version.

Original change's description:
> Revert "jni_generator: Revamp CLI"
>
> This reverts commit 0324ff816d24325dcb5cf1348f52d4fe789954ee.
>
> Reason for revert: #gardener Blocking CrOS uprev since https://crrev.com/c/4688602
> jni_zero.py:138 "TypeError: __init__() got an unexpected keyword argument 'required'"
>
> Bug: 1465241
>
> Original change's description:
> > jni_generator: Revamp CLI
> >
> > There is now one script with two subcommands:
> >  * jni_zero.py generate-library (for jni_generator.py)
> >  * jni_zero.py generate-final (for jni_registration_generator.py)
> >
> > Other changes:
> > * Use hyphens in all flags names instead of _
> > * Remove unused --cpp flag
> > * Remove --ptr_type (we always set it to "long")
> > * Rename --include -> --extra-include
> > * Remove default value for 'javap' (to break a dep on build_utils.py)
> > * Rename jni_generator_tests.py -> integration_tests.py
> >
> > Bug: 1406605
> > Change-Id: Ie3018d6d50fc0051c39d82a580be4fd25a38f93d
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4685488
> > Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
> > Commit-Queue: Andrew Grieve <agrieve@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#1170630}
>
> Bug: 1406605
> Change-Id: I1b16d4ae07aeeb3e62e00fd25e7986fd6f699501
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4688700
> Owners-Override: Trent Apted <tapted@chromium.org>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Commit-Queue: Trent Apted <tapted@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1171021}

Bug: 1465241
Bug: 1406605
Change-Id: I78e8a03ea0580ffed28a11a723a93f07a2a353f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4695134
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1171823}

• PRESUBMIT.py[diff]
• base/android/jni_generator/PRESUBMIT.py[diff]
• base/android/jni_generator/README.md[diff]
• base/android/jni_generator/integration_tests.py[Renamed from base/android/jni_generator/jni_generator_tests.py - diff]
• base/android/jni_generator/jni_generator.py[diff]
• base/android/jni_generator/jni_generator.pydeps[Deleted - diff]
• base/android/jni_generator/jni_registration_generator.py[diff]
• base/android/jni_generator/jni_zero.py[Added - diff]
• base/android/jni_generator/jni_zero.pydeps[Renamed from base/android/jni_generator/jni_registration_generator.pydeps - diff]
• base/android/jni_generator/parse.py[diff]
• build/config/android/jni.gni[diff]
• build/config/android/rules.gni[diff]