Allow composer size to be configurable

[benparsons]

Is your suggestion related to a problem? Please describe.

Several customers complain it should be bigger. Is there some way to change constants in code to make it preexpanded to N lines and dynamically grow to M lines?

Describe the solution you'd like.

https://github.com/matrix-org/matrix-react-sdk/blob/78b1f6c0b13efd57031a329a1ac62baba948dad3/res/css/views/rooms/_SendMessageComposer.scss

Currently, the size is controlled by mx_BasicMessageComposer min-height and mx_BasicMessageComposer_input max-height, expressed in pixels. Ideally we could express this in lines of text, and have there be two variables:

• composer.initialLineHeight
• composer.maxLineHeight

Where maxLineHeight is the number of lines before scrolling begins.

Describe alternatives you've considered.

The same but still using pixels. I'd prefer lines.

Additional context

Customer ask. This is in a context where they are replacing email, rather than another chat, so needs to be larger area.

[t3chguy]

Duplicate of #5882