perf(cdkTextareaAutosize): Skip height measurements when textarea value is empty

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

Calls to _measureScrollHeight, which trigger css layout, are not needed when there's nothing in the text field. In this case, simply set the height to 1 row (height of one line).

See internal CL 421826236 for more context.

### Reproduction

Steps to reproduce:
1. Bootstrap a textarea with cdkTextareaAutosize that has value of '' (empty)

### Expected Behavior

_measureScrollHeight() called only when there's a non-empty value.

### Actual Behavior

_measureScrollHeight() is called regardless of value.

### Environment

- Angular: 13
- CDK/Material: 13
- Browser(s): All
- Operating System (e.g. Windows, macOS, Ubuntu): All

Start at the cdkTextareaAutosize implementation and trace the _measureScrollHeight entry point using a textarea whose value is empty. Confirm that empty values use a one-row height without measurement, while non-empty values retain measurement behavior; add or update the relevant test if the implementation's test location is identified.

Written by the indexing model from the issue text.