Reland "JNI Zero: Omit muxed_index param in boundary methods when unused"

This reverts commit 07787227e941bcadfc99c231edc0dd2c603fe0fb.

Reason for reland: Do not apply this for libmonochrome

Original change's description:
> Revert "JNI Zero: Omit muxed_index param in boundary methods when unused"
>
> This reverts commit 6323e91129d54eda05400b4e6d009c28ab092b1a.
>
> Reason for revert: b/380726420
> pixel4 webview tests are failing on perf waterfall.
>
> Original change's description:
> > JNI Zero: Omit muxed_index param in boundary methods when unused
> >
> > Bug: None
> > Change-Id: I4bbae41fc76418fd08791541416946f7c093ad35
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6044338
> > Commit-Queue: Sam Maier <smaier@chromium.org>
> > Auto-Submit: Andrew Grieve <agrieve@chromium.org>
> > Reviewed-by: Sam Maier <smaier@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#1386991}
>
> Bug: None
> Change-Id: I23ad128f5d1bcd8a5aaca7734f2659f1dba17c32
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6047034
> Reviewed-by: Andrew Grieve <agrieve@chromium.org>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Commit-Queue: Andrew Grieve <agrieve@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1387612}

Bug: None
Change-Id: I72aa83b08add3ca2f5880119a96526ef76787130
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6049894
Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Sam Maier <smaier@chromium.org>
Owners-Override: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1389001}