feat(core): allow independent registration and override of node/mark specs in extensions

[d3m1d0v]

Description

addNode/addMark bundle schema spec, parser spec, and serializer spec into a single callback, making it impossible for one extension to incrementally modify another — the only option was full replacement.

This PR adds granular registration and override methods to ExtensionBuilder:

New add methods:

• addNodeSpec, addMarkSpec — register ProseMirror schema specs independently
• addMarkdownTokenParserSpec — register markdown-it token → PM entity mapping
• addNodeSerializerSpec, addMarkSerializerSpec — register serializer specs

New override methods:

• overrideNodeSpec, overrideMarkSpec — modify previously registered schema specs
• overrideMarkdownTokenParserSpec — modify parser token specs (works with both addNode and granular API)
• overrideNodeSerializerSpec, overrideMarkSerializerSpec — modify serializer specs

addNode and addMark methods are marked as @deprecated.

[gravity-ui]

[gravity-ui]

[makhnatkin]

it('should preserve addNode full spec when addMarkdownTokenParserSpec uses same tokenName', () => {
    // Bug scenario: tokenName === entityName in step 1b of build()
    // Step 1 adds full spec under 'code_block'.
    // Step 1b finds parserSpecsByEntity['code_block'] and calls map.addToEnd('code_block', parserOnlyEntry),
    // which overwrites the full spec with { spec: {}, toMd: () => { throw } }.
    const realToMd = jest.fn();

    const nodes = new ExtensionBuilder(logger)
        .addNode('code_block', () => ({
            spec: {group: 'block', code: true},
            fromMd: {tokenSpec: {name: 'code_block', type: 'block', noCloseToken: true}},
            toMd: realToMd,
        }))
        .addMarkdownTokenParserSpec('code_block', () => ({
            // tokenName === entityName: 'code_block' → 'code_block'
            name: 'code_block',
            type: 'block',
            noCloseToken: true,
        }))
        .build()
        .nodes();

    // Full addNode spec must survive — not be replaced by parser-only entry
    expect(nodes.size).toBe(1);

    const codeBlock = nodes.get('code_block');
    expect(codeBlock).toBeTruthy();
    // Spec must be the real one, not {} from buildParserOnlyNodeEntry
    expect(codeBlock!.spec.group).toBe('block');
    expect(codeBlock!.spec.code).toBe(true);
    // toMd must be the real function, not the throwing stub
    expect(codeBlock!.toMd).toBe(realToMd);
    expect(() => (codeBlock!.toMd as Function)()).not.toThrow();
});

[makhnatkin]

Should we add the same checks like:

        if (this.#rawNodeSpecs[name]) {
            throw new Error(`Node spec with name "${name}" already registered via addNodeSpec`);
        }

?