Generalize swap actions

[thomaseizinger]

Instead of every client needing to repeat themselves in how specific actions are constructed from the params, we construct the action directly in the swap protocol functions and emit fairly simply actions to the caller.

This simplifies the implementation of clients driving the swap.

Additionally, this is conceptually better from the perspective of the protocol execution function. For this function to be coherent, it should control all parts that are critical to protocol. Building the actual action inside the protocol function provides this control.

[mergify[bot]]

bors r+

[bors[bot]]

Build failed:

• build (macos-latest)

[thomaseizinger]

bors retry

[bors[bot]]

Build succeeded:

• build (macos-latest)
• build (ubuntu-latest)
• build (windows-latest)
• static_analysis