[fidl] Add source information to AST

Every node in the AST is given start, end, and previous_end
information. The start and end are relatively self-explanatory. The
previous_end is the end of the last AST node in declaration order. The
space between the previous_end and start will most likely contain
any comments relevant to the node.

This may leave the AST with a trail of stuff (whitespace, comments) that
is stored in the top level AST node (File).

Test: A visitor will be added in a subsequent CL. It will have a test
that ensures you can reconstruct the original file.

Change-Id: I3f7dcd7d8ca124042679b1b01e8dd0cada270825

[fidl] Make token kind enum match the style guide

Change-Id: I5d69b577f5806c62bd7245a950c2d4e842322b08

[fidl] Clang format again, this time with column-limit 100 set

Change-Id: Id87234e4cc33b300445b755a738cff214a33fc0e

[build][fidl] Separate the fidl (host) lib from the compiler binary.

TO-732

Change-Id: I02625c25d3cac7bb7316370c47c765e1a66e9a01

[fidl] Add a notion of SourceLocation, and use it in a bit of error reporting

Change-Id: Ie27a04dcd83d639ca2d4a029773c4d6bdadee1e3

[fidl] Rename token_definitions.h to .inc

This is designed to be included multiple times for different X macros,
so name it accordingly.

Change-Id: I1899577dfffb828d3845bc0d6ebc4ebd0f79a179

[fidl][host] Tweak the fidl host tool build layout

Many of these files are consumed by a currently disabled Garnet gn
target (it is disabled until a future toolchain roll fixes some
fuzzing support infrastructure), which essentially builds a
fuzzing-oriented version of the compiler.

The current layout is expressed as a BUILD.gn file in Zircon. When we
remove these, in favor of generated manifests, this layout will be
difficult to express. The new one puts everything but main into a
separate directory.

Change-Id: I18ea1807fa5d75a3b2620f3a54d4aac4999e0442