This PR implements the design changes for flow analysis in local
functions, specifically the decision to allow local functions to be
declared anywhere in the method and only have captured usages considered
at the local function use site, rather than the declaration site.

The key points of the algorithm are as follows:

    1. Visit local functions recursively:
        a. For each new read/write of a captured variable in the local
           function, record it. If the local function has already been used,
           mark the `stateChangedAfterUse` to `true`, indicating that we
           need to visit another pass.
        b. When a local function is used, play back the recorded
           read/writes if the variable is not still captured. Mark the local
           function as used.
    2. Process remaining statements in the parent method, performing
        (1.b) when necessary.
    3. If `stateAfterChanged` has been set to true, visit the entire method
       again (and go to 1).

Fixes #10391.