Modularize the WASM kernels into separate build targets.

[nsthorat]

• Each kernel gets its own cc_library and file.
• A new cc_library encapsulates all of them: ":all_kernels"
• backend.cc contains global state and backend utilities.
• Add linkstatic=1 so the compiler yells before emscripten fails at linking (it doesn't support dynamic linking, e.g. extern globals).

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This change is 

[dsmilkov]

Reviewed 3 of 10 files at r1.
Reviewable status: 0 of 1 approvals obtained (waiting on @dsmilkov and @nsthorat)

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tfjs-backend-wasm/src/cc/backend.cc, line 30 at r1 (raw file):

std::map<int, TensorInfo> data;

TensorInfo get_tensor_info(int tensor_id) { return data.at(tensor_id); }

make get_tensor_info() which is a public api live under tfjs/backend namespace , not just tfjs
This way other files that include backend.h can call backend::get_tensor_info which tells you from which file those imports came.
https://google.github.io/styleguide/cppguide.html#Namespaces

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tfjs-backend-wasm/src/cc/kernels.h, line 15 at r1 (raw file):

 * ===========================================================================*/

#ifndef TFJS_WASM_KERNELS_H_

make sure each new file has these guards to defend against duplicate code.
https://google.github.io/styleguide/cppguide.html#The__define_Guard

[dsmilkov]

Reviewable status: 0 of 1 approvals obtained (waiting on @nsthorat)

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tfjs-backend-wasm/src/cc/backend.cc, line 28 at r1 (raw file):

// Maps a unique tensor id to info about that tensor. The map owns all of its
// entries.
std::map<int, TensorInfo> data;

move data to unnamed namespace which makes it truly private. see https://google.github.io/styleguide/cppguide.html#Unnamed_Namespaces_and_Static_Variables

[nsthorat]

Reviewable status: 0 of 1 approvals obtained (waiting on @dsmilkov)

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tfjs-backend-wasm/src/cc/backend.cc, line 28 at r1 (raw file):

Previously, dsmilkov (Daniel Smilkov) wrote…

move data to unnamed namespace which makes it truly private. see https://google.github.io/styleguide/cppguide.html#Unnamed_Namespaces_and_Static_Variables

Done

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tfjs-backend-wasm/src/cc/backend.cc, line 30 at r1 (raw file):

Previously, dsmilkov (Daniel Smilkov) wrote…

make get_tensor_info() which is a public api live under tfjs/backend namespace , not just tfjs
This way other files that include backend.h can call backend::get_tensor_info which tells you from which file those imports came.
https://google.github.io/styleguide/cppguide.html#Namespaces

Done

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tfjs-backend-wasm/src/cc/kernels.h, line 15 at r1 (raw file):

Previously, dsmilkov (Daniel Smilkov) wrote…

make sure each new file has these guards to defend against duplicate code.
https://google.github.io/styleguide/cppguide.html#The__define_Guard

all new .h files have this already :)

[dsmilkov]

Reviewed 4 of 10 files at r1, 4 of 4 files at r2.
Reviewable status: complete! 1 of 1 approvals obtained