Switches generated text protos to use {...} instead of <...>.
No other observable changes.

TBR=yiwzhang@google.com

Change-Id: Ifcbb6f0ba891c23676bc1562fcf65aa54b00e9d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2235969Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>