jellyroll: change tab slider padding

The tab slider button text is elided after adding 4 tabs on VC panel.

The cl updates the tab padding to leave more space for the label. The
effects before and after change are shown in the bug comment.

Bug: b:331827366
Change-Id: I57b0c365f64b42fd68c32ccabb176777023bf093
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5406297


Commit-Queue: Xiaodan Zhu <zxdan@chromium.org>
Reviewed-by: Jiaming Cheng <jiamingc@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280325}