Merge remote-tracking branch 'cros/upstream' into 'cros/master'

Following commits are included:
ef133a7 libmbim-glib,device: avoid using an already unref-ed source
3d397f8 libmbim-glib: drop GUdev optional build dependency
aff2313 libmbim-glib,device: realpath() returns NULL if path doesn't exist
f007997 libmbim-glib,device: don't warn if descriptors file cannot be read
8373678 build: fix distcheck with new gtk-doc
d0ecfda build: update builtin gtk-doc support
fe83ee4 sar: new service
c9f0a32 build,codegen: avoid using ${name}s
2584a18 docs: add API index for 1.26
1885243 build: bump version to 1.25.1 to flag existence of new API (SAR service)
aadfcd4 sar: untabify JSON database
4545505 sar: remove the "Notification" of MBIM_CID_MS_SAR_CONFIG

BUG=None
TEST=Install on hatch. Verify cellular connection.

Change-Id: I7919dce35fe9c79a1e849e58938d6061d1e799d3