Update minimum Node.js version to 15.0.0

This is about 2 years old, and the node website already provides newer versions both
for latest and for LTS. However, other places are behind, for example the latest
Ubuntu LTS (22) has Node 12, so perhaps we should wait on this.

This is possible after emscripten-core/emsdk#829 made the emsdk
install a 15.x version by default.

ChangeLog.md

@@ -18,6 +18,11 @@ to browse the changes between the tags.
 
 See docs/process.md for more on how version tagging works.
 
+Future
+-----
+- Bump the default minimum Node version from 10.19 to 15.0. To target the
+  previous minimum version (10.19.0), use `-sMIN_NODE_VERSION=101900`.
+
 3.1.36 (in development)
 -----------------------
 - The `USES_DYNAMIC_ALLOC` setting has been deprecated.  You can get the same

src/settings.js

@@ -1796,7 +1796,7 @@ var MIN_CHROME_VERSION = 75;
 // distinct from the minimum version required run the emscripten compiler.
 // This version aligns with the current Ubuuntu TLS 20.04 (Focal).
 // Version is encoded in MMmmVV, e.g. 1814101 denotes Node 18.14.01.
-var MIN_NODE_VERSION = 101900;
+var MIN_NODE_VERSION = 150000;
 
 // Tracks whether we are building with errno support enabled. Set to 0
 // to disable compiling errno support in altogether. This saves a little