feat(ecode): add VS Code-compatible user snippets

Add user-defined snippet support to the autocomplete plugin, including
language-specific, global, .vscode, and .ecode project snippets.

Support JSONC parsing, scopes, hot reload, source-aware ranking, exact
prefix replacement, multi-cursor insertion, contextual indentation,
variables, transforms, choices, linked placeholders, and tab navigation.

Recognize .code-snippets files as JSON and preserve existing LSP snippet
completion behavior.

Refs SpartanJ/ecode#111

src/tools/ecode/jsonhelper.cpp

@@ -0,0 +1,87 @@
+#include "jsonhelper.hpp"
+
+namespace {
+
+static size_t nextJSONToken( std::string_view contents, size_t pos ) {
+	while ( pos < contents.size() ) {
+		while ( pos < contents.size() && ( contents[pos] == ' ' || contents[pos] == '\t' ||
+										   contents[pos] == '\r' || contents[pos] == '\n' ) )
+			++pos;
+		if ( pos + 1 >= contents.size() || contents[pos] != '/' )
+			break;
+		if ( contents[pos + 1] == '/' ) {
+			pos += 2;
+			while ( pos < contents.size() && contents[pos] != '\n' )
+				++pos;
+		} else if ( contents[pos + 1] == '*' ) {
+			pos += 2;
+			while ( pos + 1 < contents.size() &&
+					!( contents[pos] == '*' && contents[pos + 1] == '/' ) )
+				++pos;
+			if ( pos + 1 < contents.size() )
+				pos += 2;
+		} else {
+			break;
+		}
+	}
+	return pos;
+}
+
+} // namespace
+
+std::string json_strip_trailing_commas( std::string_view contents ) {
+	std::string sanitized;
+	sanitized.reserve( contents.size() );
+	bool inString = false;
+	bool escaped = false;
+	bool lineComment = false;
+	bool blockComment = false;
+	for ( size_t pos = 0; pos < contents.size(); ++pos ) {
+		const char ch = contents[pos];
+		if ( lineComment ) {
+			lineComment = ch != '\n';
+			sanitized.push_back( ch );
+			continue;
+		}
+		if ( blockComment ) {
+			if ( ch == '*' && pos + 1 < contents.size() && contents[pos + 1] == '/' ) {
+				blockComment = false;
+				sanitized += "*/";
+				++pos;
+			} else {
+				sanitized.push_back( ch );
+			}
+			continue;
+		}
+		if ( inString ) {
+			sanitized.push_back( ch );
+			if ( escaped )
+				escaped = false;
+			else if ( ch == '\\' )
+				escaped = true;
+			else if ( ch == '"' )
+				inString = false;
+			continue;
+		}
+		if ( ch == '"' ) {
+			inString = true;
+			sanitized.push_back( ch );
+			continue;
+		}
+		if ( ch == '/' && pos + 1 < contents.size() ) {
+			if ( contents[pos + 1] == '/' )
+				lineComment = true;
+			else if ( contents[pos + 1] == '*' )
+				blockComment = true;
+			sanitized.push_back( ch );
+			continue;
+		}
+		if ( ch == ',' ) {
+			const size_t next = nextJSONToken( contents, pos + 1 );
+			if ( next < contents.size() && ( contents[next] == '}' || contents[next] == ']' ) )
+				continue;
+		}
+		sanitized.push_back( ch );
+	}
+	return sanitized;
+}