feat: expose nodeIsMissing getter

[char0n]

During my research into tree-sitter CST traversal, I found out that Node.js tree-sitter binding doesn't contain cached getter nodeIsMissing. Because of that, when using TreeCursor, the only way to determine if the SyntaxNode is missing is to call the cursor.currentNode.isMissing() method. By doing this, traversal performance goes out the window. web-binding for tree-sitter exposes nodeIsMissing cached field, but Node.js binding doesn't. This PR remedies the situation.

Before:

cursor = tree.walk();
cursor.currentNode.isMissing();

After:

cursor = tree.walk();
cursor.nodeIsMissing;

Refs tree-sitter/tree-sitter#1469

Signed-off-by: Vladimir Gorej vladimir.gorej@gmail.com

[char0n]

Tests are failing on x86 Platform, but pass on x64. Have no idea why thought.

[char0n]

@maxbrunsfeld just pinging here

[char0n]

@maxbrunsfeld pinging again.

[char0n]

@maxbrunsfeld just pinging again