[roll] Roll fuchsia [ffx][config] Fix host tool resolution for subtools

When ffx_build_dual_mode_plugins_as_subtools = true is set, the emu
plugin is executed as an independent external subtool binary
(host-tools/ffx-emu). Under this configuration, the sdk.get_host_tool
lookup fails because in-tree builds do not generate a standard
meta/manifest.json directly in the build output directory.

When this fails, the engine falls back to locating host tools relative
to the running executable. However, binaries under host-tools/ are
hard links to the corresponding host_x64/ or host_arm64/ files.
Because standard filesystems cannot trace back-links from hard-link paths,
canonicalizing the executable returns host-tools/ffx-emu. The stopgap then
joins "zbi" to the parent (host-tools/), which fails because zbi is only present
in the host_x64/ or host_arm64/ directory.

This change fixes the root cause by correcting SdkRoot resolution in-tree. If
ffx is executing inside a Fuchsia source tree and has a build directory
configured, we resolve the SdkRoot directly to the host-architecture tools
directory (e.g., build_dir/host_x64 or build_dir/host_arm64) if it exists. This
ensures that sdk.get_host_tool resolves companion tools correctly in-tree for
both monolith and subtool executions.

Original-Original-Bug: 494668641
Test: fx test host_x64/ffx_emulator_start_lib_test
Test: fx test host_x64/ffx_config_lib_test
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1636179
Original-Original-Revision: f77da07000ea4d93cbef2106c9af9938af6359d3
GitOrigin-RevId: 2eb9371a466148ba54cf04e96f2c2ad330a5e493
Change-Id: I25b56c104927c18fd21addcd493164d63afd3dfe
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1636795
Cr-Commit-Position: refs/heads/main@{#193940}