Fix clunky amount input field

[TorstenStueber]

The input field for the input amount has some clunky UX.

For example,

• if the input is "0.12" and the user marks the text and presses "1", then
  • expected: the content of the input field changes to "1"
  • actually: the content of the input field changes to "0.11"
• if the input is "0.12" and the user types ".", then
  • expected: ignore the input
  • actually: the content changes to "0.1"
• if the input is "0.23" and the cursor is between "0" and "." and the user enters "2"
  • expected: input changes to "02.23"
  • actually: input changes to "0.22"
• if the input is "0.23" and the cursor is between "." and "2" and the user enters "4"
  • expected: input changes to "0.42"
  • actually: input changes to "0.24"

A mostly correct implementation of this logic is the handleOnChangeNumericInput function in the Portal.

I say mostly correct because that implementation has unexpected results when a user enters "." when there is already a "." in the input:

• if the user input is "0.23" and the cursor is between "2" and "3" and the user enters "."
  • expected: ignore the input as there is already one "." in the input field further to the left
  • actual: input changes to "0.2"
• if the user input is "12.34" and the cursor is between "1" and "2" and the user enters "."
  • expected: either ignore the input as there is already a "." in the input field further to the right or replace input to "1.234"
  • actual" input changes to "1.2"

TODO

Implement the input handling so that all cases above behave like as expected.

[TorstenStueber]

Hey team! Please add your planning poker estimate with Zenhub @b-yap @bogdanS98 @ebma @gianfra-t @Sharqiewicz

[Sharqiewicz]

@TorstenStueber Thanks for noticing these edge cases for NumericInput. I think they definitely need to be added to NumericInput.test.tsx in Portal. I think we should make the changes in Portal as well. I have created a PR that fixes these errors and creates test cases here: https://github.com/pendulum-chain/portal/pull/561. Can we just copy this into Vortex?