Update internal use of decimal to float (#10333)

# Description
We made the decision that our floating point type should be referred to
as `float` over `decimal`.
Commands were updated by #9979 and #10320

Now make the internal codebase consistent in referring to this data type
as `float`.

Work for #10332

# User-Facing Changes

`decimal` has been removed as a type name/symbol. 

Instead of 
```nushell
def foo [bar: decimal] decimal -> decimal {}
```
use 
```nushell
def foo [bar: float] float -> float {}
```

Potential effect of `SyntaxShape`'s `Display` implementation now also
referring to `float` instead of `decimal`

# Details
- Rename `SyntaxShape::Decimal` to `Float`
- Update `Display for SyntaxShape` to `float`
- Update error message + fn name in dataframe code
- Fix docs in command examples
- Rename tests that are float specific
- Update doccomment on `SyntaxShape`
- Update comment in script

# Tests + Formatting
Updates the names of some tests

crates/nu-protocol/src/syntax_shape.rs

@@ -31,9 +31,6 @@ pub enum SyntaxShape {
     /// A datetime value, eg `2022-02-02` or `2019-10-12T07:20:50.52+00:00`
     DateTime,
 
-    /// A decimal value, eg `1.0`
-    Decimal,
-
     /// A directory is allowed
     Directory,
 
@@ -52,6 +49,9 @@ pub enum SyntaxShape {
     /// A filesize value is allowed, eg `10kb`
     Filesize,
 
+    /// A floating point value, eg `1.0`
+    Float,
+
     /// A dotted path to navigate the table (including variable)
     FullCellPath,
 
@@ -82,7 +82,7 @@ pub enum SyntaxShape {
     /// Nothing
     Nothing,
 
-    /// Only a numeric (integer or decimal) value is allowed
+    /// Only a numeric (integer or float) value is allowed
     Number,
 
     /// One of a list of possible items, checked in order
@@ -137,7 +137,7 @@ impl SyntaxShape {
             SyntaxShape::Expression => Type::Any,
             SyntaxShape::Filepath => Type::String,
             SyntaxShape::Directory => Type::String,
-            SyntaxShape::Decimal => Type::Float,
+            SyntaxShape::Float => Type::Float,
             SyntaxShape::Filesize => Type::Filesize,
             SyntaxShape::FullCellPath => Type::Any,
             SyntaxShape::GlobPattern => Type::String,
@@ -189,7 +189,7 @@ impl Display for SyntaxShape {
             SyntaxShape::Number => write!(f, "number"),
             SyntaxShape::Range => write!(f, "range"),
             SyntaxShape::Int => write!(f, "int"),
-            SyntaxShape::Decimal => write!(f, "decimal"),
+            SyntaxShape::Float => write!(f, "float"),
             SyntaxShape::Filepath => write!(f, "path"),
             SyntaxShape::Directory => write!(f, "directory"),
             SyntaxShape::GlobPattern => write!(f, "glob"),