[piexwasm] Release piexwasm at emscripten 1.38.33

 ◑ Install upstream emscripten at version 1.38.33 (git hash 7e841b5)
 ◑ Pull upstream android.googlesource.com PIEX (git hash 6672dab)
 ◑ % make clean && make, run tests PASS
 ◑ Binary size: reduced by 1.3 kByte
 ◑ Assess performance: unchanged

Test: browser_tests --gtest_filter="QuickView*FilesAppBrowserTest*"
Bug: 1132695

Change-Id: I52787b1b9ac31a927899672261895037e8cc3bbf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2460570Reviewed-by: Alex Danilo <adanilo@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815044}

ui/file_manager/image_loader/piex/README.md

@@ -3,8 +3,8 @@ Install emscripten https://emscripten.org/docs/getting_started/index.html
 ```shell
   git clone https://github.com/emscripten-core/emsdk.git
   cd emsdk
-  ./emsdk install 1.38.27
-  ./emsdk activate 1.38.27
+  ./emsdk install 1.38.33
+  ./emsdk activate 1.38.33
   source ./emsdk_env.sh
 ```
 
@@ -34,4 +34,4 @@ Release: submit piex.js.wasm piex.out.wasm to the Chromium repository
   git cl upload
 ```
 
-Release Builder: emscripten 1.38.27
+Release Builder: emscripten 1.38.33