[view-compiler] Support method declaration and invocation in Dex builder

The Dex builder can now generate calls to methods (although not in all forms
yet). To help do this, we add a new virtual Instruction and Value class. This is
needed to generate code with values that are not known until the entire method
has been generated. In particular, we can now refer to function parameters.

The test method now accepts a String and returns the the length of the string.

Bug: 111895153
Change-Id: I11d52b083ae51d8151fccb1a65e45d40ff05fd81