[Bug] PrivateIdentifier nodes are omitted from 2020 semantic classifications

# Bug Report

### 🔎 Search Terms

semantic highlighting, semantic token, PrivateIdentifier, private field, private method, encodedSemanticClassifications

### 🕗 Version & Regression Information

- TypeScript 6.0.3 (bundled with VS Code)
- Also present in the v5.9 classifier implementation
- This is not a theme-specific issue

### 💻 Code

```ts
class Foo {
field = 1;
#privateField = 1;

method() {}
#privateMethod() {}

test() {
this.field;
this.#privateField;

this.method();
this.#privateMethod();
}
}
```

### 🙁 Actual behavior

In VS Code's **Developer: Inspect Editor Tokens and Scopes**:

- `field` and `method` receive semantic token types.
- `#privateField` and `#privateMethod` receive no semantic token and fall back to TextMate scopes.
- As a result, `editor.semanticTokenColorCustomizations` rules for `property` and `method` do not apply to ECMAScript private members.

### 🙂 Expected behavior

- `#privateField` should be classified as `property`.
- `#privateMethod` should be classified as `method`.
- Declarations should also receive the `declaration` modifier.

### Root cause

VS Code requests `encodedSemanticClassifications-full` with format `"2020"`.

In `src/services/classifier2020.ts`, `collectTokens` only enters the semantic-classification path for `isIdentifier(node)`:

```ts
if (isIdentifier(node) && ...) {
let symbol = typeChecker.getSymbolAtLocation(node);
// ...
}
```

ECMAScript private names are separate `SyntaxKind.PrivateIdentifier` nodes, so they are skipped before `getSymbolAtLocation` is called.

Relevant source:
https://github.com/microsoft/TypeScript/blob/050880ce59e30b356b686bd3144efe24f875ebc8/src/services/classifier2020.ts#L121-L203

### Proposed fix

```diff
+ isPrivateIdentifier,
isPropertyAccessExpression,
```

```diff
- if (isIdentifier(node) && ...) {
+ if ((isIdentifier(node) || isPrivateIdentifier(node)) && ...) {
```

The existing declaration-kind mapping already classifies private fields and methods correctly once these nodes reach the symbol-classification path.

I tested the equivalent change against TypeScript 6.0.3:

- `#privateField` declaration/reference → `property`
- `#privateMethod` declaration/reference → `member` internally, mapped by VS Code to `method`
- declaration occurrences receive the `declaration` modifier
- added fourslash regression test passes

### Related issue

https://github.com/microsoft/TypeScript/issues/44483 requests new `private`/`protected` semantic modifiers. This report is different: ECMAScript `PrivateIdentifier` nodes currently receive no semantic classification at all.

Start in src/services/classifier2020.ts at collectTokens and review the existing declaration-kind mapping for identifier nodes. Add the relevant fourslash regression test covering private field and method declarations and references, then verify that the nodes receive property or method classifications and declaration modifiers.

Written by the indexing model from the issue text.